Add speech recognition context to the Web Speech API

[yrw-google]

Explainer for speech recognition context is added in #140

This PR should be updated and merged after the explainer is approved and merged.

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[yrw-google]

Hi @padenot, can you review this one too and also take a look at the explainer again when you get a chance? Feel free to assign another reviewer too if needed

[padenot]

This is invalid WebIDL.

It would be either:

SpeechRecognition item(unsigned long index);

or

getter SpeechRecognition(unsigned long index)

What is the intent here?

[yrw-google]

I've changed this to SpeechRecognitionPhrase item(unsigned long index), but using getter is actually how SpeechRecognitionResultList is doing it, as well as some list objects I've seen in other specs, e.g. https://html.spec.whatwg.org/multipage/common-dom-interfaces.html#the-domstringlist-interface. I thought it's a standard thing to always define a getter for a list, but I don't see that getter is required in our use case, so I can either keep it or remove it.

[yrw-google]

Hi @padenot, I've updated the specs as well as the explainer according to your comments. Please take a look again when you get a chance. Thanks!

[padenot]

Can we please focus on either the explainer or the spec patch? If we have a spec patch, an explainer shouldn't be necessary. If we aren't comfortable writing the spec patch right now because we want to iterate, it doesn't seem useful to update the spec patch.

Let me know which one I should look at first please?

[yrw-google]

Hi @padenot, you can focus on the spec patch right now. I'm keeping the spec patch and the explainer in sync and the spec patch has many more details than the explainer, so if we can reach consensus on the spec, we can also reach consensus on the explainer easily.

I think the explainer is still necessary when we want to launch this feature since we will be asked for a link to an explainer in many places. The explainer is also a good place to show why we want to add contextual biasing, and provides brief introduction on the changes for people who don't want to learn about every detail in specs.