Add gamepad light indicator extension

[fernando-80]

Closes #67

The following tasks have been completed:

• Modified Web platform tests (link to pull request)

Implementation commitment:

• WebKit (https://bugs.webkit.org/show_bug.cgi?id=)
• Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
• Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=1523351)

[fernando-80]

@nondebug @knyg @sagoston light-indicator extension PR ^^^

[marcoscaceres]

Hi @fernando-80, could you kindly please join the WebApps working group? That will make the IPR bot happy.

[marcoscaceres]

I don't know if this can be guaranteed to succeed. @nondebug, do you have an opinion about this?

[nondebug]

We typically don't get a signal that the color was changed successfully so we shouldn't claim that in the spec. I think we should reword this so we resolve when the LED color change command is sent and reject if the command couldn't be sent.

[marcoscaceres]

Ok, so yeah... it shouldn't resolve with true either.

We probably need to rewrite this whole section. I'd suggest having a look at:
https://w3c.github.io/web-share/#share-method

Basically, we need to do a few checks that can cause the promise to reject... the controller has been disconnected/no longer available, etc. There might be a SecurityError if the permission has been changed before .setColor() is called. Also, what should happen if:

while (true) {
   x.setColor(randomRGB());
}

Rate limit? Drop requests on the floor?

[nondebug]

We discussed this and couldn't come up with any compelling reasons to keep the Promise. It's unlikely that we'll receive any error indication from the device and there isn't any way we can lose permission for a Gamepad. Let's remove the promise and treat setColor as fire-and-forget.

[marcoscaceres]

This needs to reject with a an actual DOM Exception of some kind. I think this is overly broad/underspecified tho...

[marcoscaceres]

Thanks @fernando-80! Some suggestions...

[marcoscaceres]

Suggested change

	The returned Promise will resolve <code>true</code> when setting the
	The returned Promise will resolve `undefined` when setting the

[marcoscaceres]

We should investigate what existing color objects we could use from the platform here.

[willuhmjs]

Looks good, excited for this feature.