Update accessibility documentation.

Move existing overview to accessibility/ subdirectory and make
accessibility.md a table of contents.

Migrate ChromeVox documentation to markdown.
Add new documentation for PATTS and BRLTTY.
Update accessibility LayoutTests documentation.

BUG=none
[email protected],[email protected]
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Review-Url: https://codereview.chromium.org/2701603002
Cr-Commit-Position: refs/heads/master@{#450865}

docs/accessibility/brltty.md

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+# BRLTTY in Chrome OS
+
+Chrome OS uses the open-source [BRLTTY](http://mielke.cc/brltty/)
+library to provide support for refreshable braille displays.
+
+We typically ship with a stable release build of BRLTTY plus some
+cherry-picked patches.
+
+## Updating BRLTTY or adding a patch
+
+First, follow the public
+[Chromium OS Developer Guide](http://www.chromium.org/chromium-os/developer-guide) to check out the source.
+At a minimum you'll need to create a chroot.
+You do not need to build everything from source.
+You do need to start the devserver.
+
+Next, flash your device to a very recent test build. Internally at Google
+you can do this with the following command when the dev server is running,
+where CHROMEBOOK_IP_ADDRESS is the IP address of your Chromebook already
+in developer mode, and $BOARD is your Chromebook's board name.
+
+```cros flash ssh://CHROMEBOOK_IP_ADDRESS xbuddy://remote/$BOARD/latest-dev/test```
+
+The BRLTTY files can be found in this directory:
+
+```third_party/chromiumos-overlay/app-accessibility/brltty```
+
+The first thing you'll need to do is edit the ebuild symlink to change the
+revision number. The real file is something like brltty-5.4.ebuild,
+but the revision will be something like brltty-5.4-r5.ebuild. You'll need
+to increment it.
+
+To increment it from r5 to r6, you'd do something like this:
+
+```
+rm brltty-5.4-r5.ebuild
+ln -s brltty-5.4.ebuild brltty-5.4-r6.ebuild
+git add brltty-5.4-r6.ebuild
+```
+
+The changes we make are all patches against a stable release of brltty.
+To add a new patch, put it in the files/ directory and reference it in
+brltty.bashrc
+
+Once you're done adding patches or making other changes, flash it to your
+device like this:
+
+```
+emerge-$BOARD brltty
+cros deploy CHROMEBOOK_IP_ADDRESS brltty
+```
+
+After that, reboot your Chromebook and verify that brltty works.
+
+To upload a change, use repo, something like this:
+
+```
+repo start <branch_name> .
+git commit -a
+  BUG=chromium:12345
+  TEST=Write what you tested here
+repo upload .
+```
+
+Note that you shouldn't need to run cros_workon.

docs/accessibility/chromevox.md

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+# ChromeVox (for developers)
+
+ChromeVox is the built-in screen reader on Chrome OS. It was originally
+developed as a separate extension but now the code lives inside of the Chromium
+tree and it's built as part of Chrome OS.
+
+To start or stop ChromeVox on Chrome OS, press Ctrl+Alt+Z at any time.
+
+## Developer Info
+
+Code location: ```chrome/browser/resources/chromeos/chromevox```
+
+Ninja target: it's built as part of "chrome", but you can build and run
+chromevox_tests to test it (Chrome OS target only - you must have target_os =
+"chromeos" in your GN args first).
+
+## Developing On Linux
+
+ChromeVox for Chrome OS development is done on Linux.
+
+See [ChromeVox on Desktop Linux](chromevox_on_desktop_linux.md)
+for more information.
+
+## ChromeVox Next
+
+ChromeVox Next is the code name we use for a major new rewrite to ChromeVox that
+uses the automation API instead of content scripts. The code is part of
+ChromeVox (unique ChromeVox Next code is found in
+chrome/browser/resources/chromeos/chromevox/cvox2).
+
+ChromeVox contains all of the classic and next code in the same codebase, it
+switches its behavior dynamically based on the mode:
+
+* Next: as of version 56 of Chrome/Chrome OS, this is default. ChromeVox uses new key/braille bindings, earcons, speech/braille output style, the Next engine (Automation API), and other major/minor improvements
+* Next Compat: in order to maintain compatibility with some clients of the ChromeVox Classic js APIs, some sites have been whitelisted for this mode. ChromeVox will inject classic content scripts, but expose a Next-like user experience (like above)
+* Classic: as of version 56 of Chrome/Chrome OS, this mode gets enabled via a keyboard toggle Search+Q. Once enabled, ChromeVox will behave like it did in the past including keyboard bindings, earcons, speech/braille output style, and the underlying engine (content scripts).
+* Classic compat for some sites that require Next, while running in Classic, ChromeVox will use the Next engine but expose a Classic user experience (like above)
+
+Once it's ready, the plan is to retire everything other than Next mode.
+
+## ChromeVox Next
+
+To test ChromeVox Next, click on the Gear icon in the upper-right of the screen
+to open the ChromeVox options (or press the keyboard shortcut Search+Shift+O, O)
+and then click the box to opt into ChromeVox Next.
+
+If you are running m56 or later, you already have ChromeVox Next on by
+default. To switch back to Classic, press Search+Q.
+
+## Debugging ChromeVox
+
+There are options available that may assist in debugging ChromeVox. Here are a
+few use cases.
+
+### Feature development
+
+When developing a new feature, it may be helpful to save time by not having to
+go through a compile cycle. This can be achieved by setting
+```chromevox_compress_js``` to 0 in
+chrome/browser/resources/chromeos/chromevox/BUILD.gn, or by using a debug build.
+
+In a debug build or with chromevox_compress_js off, the unflattened files in the
+Chrome out directory (e.g. out/Release/resources/chromeos/chromevox/). Now you
+can hack directly on the copy of ChromeVox in out/ and toggle ChromeVox to pick
+up your changes (via Ctrl+Alt+Z).
+
+### Fixing bugs
+
+The easiest way to debug ChromeVox is from an external browser. Start Chrome
+with this command-line flag:
+
+```out/Release/chrome --remote-debugging-port=9222```
+
+Now open http://localhost:9222 in a separate instance of the browser, and debug the ChromeVox extension background page from there.
+
+Another option is to use emacs jade (available through -mx
+package-list-packages).
+
+It also talks to localhost:9222 but integrates more tightly into emacs instead.
+
+Another option is to use the built-in developer console. Go to the
+ChromeVox options page with Search+Shift+o, o; then, substitute the
+“options.html” path with “background.html”, and then open up the
+inspector.
+
+### Running tests
+
+Build the chromevox_tests target. To run
+lots of tests in parallel, run it like this:
+
+```out/Release/chromevox_tests --test-launcher-jobs=20```
+
+Use a test filter if you only want to run some of the tests from a
+particular test suite - for example, most of the ChromeVox Next tests
+have "E2E" in them (for "end-to-end"), so to only run those:
+
+```out/Release/chromevox_tests --test-launcher-jobs=20 --gtest_filter="*E2E*"```
+
+## ChromeVox for other platforms
+
+ChromeVox can be run as an installable extension, separate from a
+linux Chrome OS build.
+
+### From source
+
+chrome/browser/resources/chromeos/chromevox/tools has the required scripts that pack ChromeVox as an extension and make any necessary manifest changes.
+
+### From Webstore
+
+Alternatively, the webstore has the stable version of ChromeVox.
+
+To install without interacting with the webstore UI, place the
+following json block in
+/opt/google/chrome-unstable/extensions/kgejglhpjiefppelpmljglcjbhoiplfn.json
+
+```
+{
+"external_update_url": "https://clients2.google.com/service/update2/crx"
+}
+```
+
+If you're using the desktop Linux version of Chrome, we recommend you
+use Voxin for speech. Run chrome with: “google-chrome
+--enable-speech-dispatcher” and select a voice provided by the speechd
+package from the ChromeVox options page (ChromeVox+o, o). As of the
+latest revision of Chrome 44, speechd support has become stable enough
+to use with ChromeVox, but still requires the flag.
+
+In the ChromeVox options page, select the flat keymap and use sticky
+mode (double press quickly of insert) to emulate a modal screen
+reader.

docs/accessibility/chromevox_on_desktop_linux.md

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+# ChromeVox on Desktop Linux
+
+## Starting ChromeVox
+
+On Chrome OS, you can enable spoken feedback (ChromeVox) by pressing Ctrl+Alt+Z.
+
+If you have a Chromebook, this gives you speech support built-in. If you're
+building Chrome from source and running it on desktop Linux, speech and braille
+won't be included by default. Here's how to enable it.
+
+## Compiling the Chrome OS version of Chrome
+
+First follow the public instructions for
+[Chrome checkout and build](https://www.chromium.org/developers/how-tos/get-the-code).
+
+Create a GN configuration with "chromeos" as the target OS, for example:
+
+```> gn args out/ChromeOSRelease```
+
+...in editor, add this line:
+
+```
+target_os = "chromeos"
+is_component_build = true
+is_debug = false
+```
+
+Note: Only ```target_os = "chromeos"``` is required, the others are recommended
+for a good experience but you can configure Chrome however you like otherwise.
+Note that Native Client is required, so do not put enable_nacl = false in
+your file anywhere!
+
+Now build Chrome as usual, e.g.:
+
+```ninja -C out/cros chrome```
+
+And run it as usual to see a mostly-complete Chrome OS desktop inside
+of a window:
+
+```out/cros/chrome```
+
+By default you'll be logged in as the default user. If you want to
+simulate the login manager too, run it like this:
+
+```out/cros/chrome --login-manager```
+
+You can run any of the above under it’s own X session (avoiding any
+window manager key combo conflicts) by doing something like
+
+```startx out/cros/chrome```
+
+## Speech
+
+If you want speech, you just need to copy the speech synthesis data
+files to /usr/share like it would be on a Chrome OS device:
+
+```
+git clone https://chromium.googlesource.com/chromiumos/platform/assets
+sudo cp assets /usr/share/chromeos-assets
+```
+
+Next, move to that directory and unzip the NaCl executables. You only need
+to do the one for your host architecture:
+
+```
+cd /usr/share/chromeos-assets/speech_synthesis/patts
+unzip tts_service_x86-64.nexe.zip
+```
+
+Finally, fix the permissions:
+
+```
+sudo chmod oug+r -R /usr/share/chromeos-assets
+```
+
+**Be sure to check permissions of /usr/share/chromeos-assets, some
+  users report they need to chmod or chown too, it really depends
+  on your system.**
+
+After you do that, just run "chrome" as above
+(e.g. out/cros/chrome) and press Ctrl+Alt+Z, and you should hear it
+speak! If not, check the logs.
+
+## Braille
+
+ChromeVox uses extension APIs to deliver braille to Brltty through
+libbrlapi and uses Liblouis to perform translation and
+backtranslation.
+
+Once built, Chrome and ChromeVox will use your machine’s running
+Brltty daemon to display braille if ChromeVox is running. Simply
+ensure you have a display connected before running Chrome and that
+Brltty is running.
+
+Testing against the latest releases of Brltty (e.g. 5.4 at time of
+writing) is encouraged.
+
+For more general information, see [ChromeVox](chromevox.md)
+
+# Using ChromeVox
+
+ChromeVox keyboard shortcuts use Search. On Linux that's usually your
+Windows key. If some shortcuts don't work, you may need to remove
+Gnome keyboard shortcut bindings, or use "startx", as suggested above,
+or remap it.
+
+* Search+Space: Click
+* Search+Left/Right: navigate linearly
+* Search+Period: Open ChromeVox menus
+* Search+H: jump to next heading on page