Enable FastMobileScrolling runtime flag for Android to match the

Enable FastMobileScrolling runtime flag for Android to match the command-line flag.

The effort needs to be done in 3 steps:
1. Create the runtime flag interface in blink;
2. Enable the flag for Android from chromium even it does not do anything in blink;
3. Replace compile time guard with runtime flag in blink and remove ENABLE_FAST_MOBILE_SCROLLING in gyp file.

This is the 2nd set of changes.

BUG=381391
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=276077

[Avi (use Gerrit), 2014-06-09 15:09:24]

lgtm

stamp

[c.shu, 2014-06-09 15:10:35]

On 2014/06/09 15:09:24, Avi wrote:
> lgtm
> 
> stamp

thank you.

[c.shu, 2014-06-09 15:10:39]

The CQ bit was checked by c.shu@samsung.com

[commit-bot: I haz the power, 2014-06-09 15:11:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/c.shu@samsung.com/324713002/1

[commit-bot: I haz the power, 2014-06-10 07:17:15]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_clang_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_clang_dbg/bui...)

[commit-bot: I haz the power, 2014-06-10 13:07:09]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-06-10 13:07:10]

Try jobs failed on following builders:
  android_clang_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_clang_dbg/bui...)

[c.shu, 2014-06-10 14:44:41]

The CQ bit was checked by c.shu@samsung.com

[commit-bot: I haz the power, 2014-06-10 14:47:03]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/c.shu@samsung.com/324713002/1

[commit-bot: I haz the power, 2014-06-10 18:06:11]

Change committed as 276077