Update accessibility related documentation to the mojo IPC

Things have changed recently and we no longer use the legacy IPC
messages to communicate between the browser and the renderer, and
we even introduce a new class (RenderAccessibilityManager), so we
need to update the documentation to keep it being accurate.

Bug: 1010831
Change-Id: Ib41883f8356c2114d17e6b606989e9a54dd54d0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2160468
Commit-Queue: Dominic Mazzoni <[email protected]>
Reviewed-by: Dominic Mazzoni <[email protected]>
Cr-Commit-Position: refs/heads/master@{#761469}

docs/accessibility/overview.md

@@ -459,9 +459,9 @@ layer translates WebAXObjects into [AXContentNodeData], which is a subclass of
 cross-platform accessibility tree. The translation is implemented in
 [BlinkAXTreeSource]. This translation happens on the renderer side, so the
 ui::AXNodeData tree now needs to be sent to the browser, which is done by
-sending [AccessibilityHostMsg_EventParams] with the payload being serialized
-delta-updates to the tree, so that changes that happen on the renderer side can
-be reflected on the browser side.
+calling the remote method [ax.mojom.RenderAccessibilityHost::HandleAXEvents()]
+with the payload being serialized delta-updates to the tree, so that changes
+that happen on the renderer side can be reflected on the browser side.
 
 On the browser side, these IPCs are received by [RenderFrameHostImpl], and then
 usually forwarded to [BrowserAccessibilityManager] which is responsible for:
@@ -477,8 +477,11 @@ usually forwarded to [BrowserAccessibilityManager] which is responsible for:
 3. Dispatching incoming accessibility actions to the appropriate recipient, via
    [BrowserAccessibilityDelegate]. For messages destined for a renderer,
    [RenderFrameHostImpl], which is a BrowserAccessibilityDelegate, is
-   responsible for sending appropriate `AccessibilityMsg_Foo` IPCs to the
-   renderer, where they will be received by [RenderAccessibilityImpl].
+   responsible for calling the remote method
+   [ax.mojom.RenderAccessibility.PerformAction()], implemented by the renderer,
+   with the appropriate payload (of type [ax.mojom.AXActionData]). This IPC call
+   will be received by [RenderAccessibilityManager], which will then relay on
+   the [RenderAccessibilityImpl] where the actual logic is implemented.
 
 On Chrome OS, RenderFrameHostImpl does not route events to
 BrowserAccessibilityManager at all, since there is no platform screenreader
@@ -507,7 +510,9 @@ which is renderer-side code, and in JavaScript by the [automation API]. The API
 is defined by [automation.idl], which must be kept synchronized with
 [ax_enums.mojom].
 
-[AccessibilityHostMsg_EventParams]: https://cs.chromium.org/chromium/src/content/common/accessibility_messages.h?sq=package:chromium&l=75
+[ax.mojom.AXActionData]: https://source.chromium.org/chromium/chromium/src/+/master:ui/accessibility/mojom/ax_action_data.mojom;l=13
+[ax.mojom.RenderAccessibilityHost::HandleAXEvents()]: https://source.chromium.org/chromium/chromium/src/+/master:content/common/render_accessibility.mojom;l=47
+[ax.mojom.RenderAccessibility.PerformAction()]: https://source.chromium.org/chromium/chromium/src/+/master:content/common/render_accessibility.mojom;l=86
 [AutomationInternalCustomBindings]: https://cs.chromium.org/chromium/src/extensions/renderer/api/automation/automation_internal_custom_bindings.h
 [AXContentNodeData]: https://cs.chromium.org/chromium/src/content/common/ax_content_node_data.h
 [AXLayoutObject]: https://cs.chromium.org/chromium/src/third_party/blink/renderer/modules/accessibility/ax_layout_object.h
@@ -525,6 +530,7 @@ is defined by [automation.idl], which must be kept synchronized with
 [ViewAccessibility]: https://cs.chromium.org/chromium/src/ui/views/accessibility/view_accessibility.h
 [Node]: https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/dom/node.h
 [RenderAccessibilityImpl]: https://cs.chromium.org/chromium/src/content/renderer/accessibility/render_accessibility_impl.h
+[RenderAccessibilityManager]: https://source.chromium.org/chromium/chromium/src/+/master:content/renderer/accessibility/render_accessibility_manager.h
 [RenderFrameHostImpl]: https://cs.chromium.org/chromium/src/content/browser/frame_host/render_frame_host_impl.h
 [ui::AXNodeData]: https://cs.chromium.org/chromium/src/ui/accessibility/ax_node_data.h
 [WebAXObject]: https://cs.chromium.org/chromium/src/third_party/blink/public/web/web_ax_object.h