Convert USE(NATIVE_FULLSCREEN_VIDEO) to a runtime enabled feature

Convert USE(NATIVE_FULLSCREEN_VIDEO) to a runtime enabled feature

This patch adds the boilerplate code to propagate command line switch to Blink,
and selectively enables alpha channel in content_shell for layout tests.

Blink patch: https://codereview.chromium.org/22454003

R=jam@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=225412

[trchen, 2013-09-12 11:01:52]

Hello reviewers,

This is a dependency of https://codereview.chromium.org/22454003 which is an
Android-specific feature, to use a separate hardware overlay for fullscreen
videos. This patch enables us to test the feature on Linux. PTAL!

[trchen, 2013-09-21 00:35:30]

Hello reviewers,
Please take a look at this patch. This patch is basically stubs that hooks up
the Blink change in https://codereview.chromium.org/22454003
Thanks!

[jam, 2013-09-23 17:52:09]

lgtm

[commit-bot: I haz the power, 2013-09-23 19:00:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/trchen@chromium.org/23597036/1

[commit-bot: I haz the power, 2013-09-23 19:39:15]

Sorry for I got bad news for ya.
Compile failed with a clobber build on android_dbg.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=android_db...
Your code is likely broken or HEAD is junk. Please ensure your
code is not broken then alert the build sheriffs.
Look at the try server FAQ for more details.

[commit-bot: I haz the power, 2013-09-24 21:02:05]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/trchen@chromium.org/23597036/1

[commit-bot: I haz the power, 2013-09-25 21:48:53]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/trchen@chromium.org/23597036/1

[commit-bot: I haz the power, 2013-09-26 02:30:01]

Sorry for I got bad news for ya.
Compile failed with a clobber build on win.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win&number...
Your code is likely broken or HEAD is junk. Please ensure your
code is not broken then alert the build sheriffs.
Look at the try server FAQ for more details.

[commit-bot: I haz the power, 2013-09-26 02:30:13]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/trchen@chromium.org/23597036/61001

[commit-bot: I haz the power, 2013-09-26 09:19:12]

Change committed as 225412