Replace compile time guard with runtime flag in blink and remove ENABLE_FAST_MOBILE_SCROLLING in gy…

Replace compile time guard with runtime flag in blink and remove ENABLE_FAST_MOBILE_SCROLLING in gyp file.

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 3rd set of changes.

BUG=381391
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175967

[tkent, 2014-06-10 23:02:40]

lgtm

[commit-bot: I haz the power, 2014-06-10 23:03:47]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/c.shu@samsung.com/323123004/20001

[commit-bot: I haz the power, 2014-06-10 23:08:28]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  blink_presubmit on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/7414)

[commit-bot: I haz the power, 2014-06-10 23:11:16]

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

[commit-bot: I haz the power, 2014-06-10 23:11:16]

Try jobs failed on following builders:
  blink_presubmit on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/7416)

[tkent, 2014-06-10 23:21:25]

Source/config.gni needs top-level owners.

[abarth-chromium, 2014-06-11 17:33:56]

lgtm

[abarth-chromium, 2014-06-11 17:34:11]

The CQ bit was checked by abarth@chromium.org

[c.shu, 2014-06-11 17:34:14]

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

[commit-bot: I haz the power, 2014-06-11 17:35:08]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/c.shu@samsung.com/323123004/20001

[commit-bot: I haz the power, 2014-06-11 17:39:01]

Change committed as 175967