Add a mediaControlsOverlayPlayButtonEnabled setting

Add a mediaControlsOverlayPlayButtonEnabled setting

This will be followed by a patch to enable the setting on Android and
then a patch to actually let the setting enable/disable the button.

BUG=366675
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172737

[philipj_slow, 2014-04-24 15:54:13]

Aaron, can you check if you think this is a good idea or not before I send all
three reviews to the appropriate reviewers?

Patch 1: this
Patch 2: https://codereview.chromium.org/257643002/
Patch 3: https://codereview.chromium.org/254633002/

[acolwell GONE FROM CHROMIUM, 2014-04-24 19:34:45]

On 2014/04/24 15:54:13, philipj wrote:
> Aaron, can you check if you think this is a good idea or not before I send all
> three reviews to the appropriate reviewers?
> 
> Patch 1: this
> Patch 2: https://codereview.chromium.org/257643002/
> Patch 3: https://codereview.chromium.org/254633002/

I wonder if
InternalSettings(https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/core/testing/InternalSettings.idl&sq=package:chromium&type=cs)
might be a better home since that appears to be for test related settings.

[philipj_slow, 2014-04-25 14:23:18]

Interesting, I didn't know about InternalSettings. It looks like it doesn't
actually hold any settings itself, it just wraps either RuntimeEnabledFeatures
or in many cases Settings itself. It isn't used from outside core/testing/ so I
don't think it would work in this case.

I don't really *need* to expose this setting to Chromium, but it's quite similar
to how mediaPlaybackRequiresUserGesture is used. Suggestions for simplification
are welcome!

[acolwell GONE FROM CHROMIUM, 2014-04-26 00:05:39]

lgtm

[philipj_slow, 2014-04-28 06:27:33]

Jochen, can you be my *.in rubber stamp?

[jochen (gone - plz use gerrit), 2014-04-28 09:21:47]

lgtm

[philipj_slow, 2014-04-28 09:35:34]

The CQ bit was checked by philipj@opera.com

[commit-bot: I haz the power, 2014-04-28 09:35:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/philipj@opera.com/250533003/1

[commit-bot: I haz the power, 2014-04-28 09:42:58]

Change committed as 172737