Add a switch to enable compositing for scrollable frames.

Add a switch to enable compositing for scrollable frames.

'--enable-accelerated-scrollable-frames'
Enabled by default on Android.

By the way, changed '--enable-accelerated-compositing-for-overflow-scroll'
to '--enable-accelerated-overflow-scroll' to make it consistent with
the other existing switches.

(The existing patterns of names:
 switch: --enable-accelerated-... or --disable-accelerated-...
 switch C++ name: kEnableAccelerated... or kDisableAccelerated...
 WebPreferences field: accelerated_compositing_for_..._enabled
 WebSettings setter: setAcceleratedCompositingFor...Enabled)

BUG=163022
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=172642

[jam, 2012-12-11 20:32:04]

lgtm

[Xianzhu, 2012-12-12 01:36:19]

@jamesr, this CL still needs an approval from you (as an owner of webkit/).

[jamesr, 2012-12-12 01:37:41]

webkit lgtm

[commit-bot: I haz the power, 2012-12-12 01:40:52]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/11543002/1

[commit-bot: I haz the power, 2012-12-12 02:50:48]

Retried try job too often on linux_chromeos for step(s) aura_unittests,
base_unittests, browser_tests, cacheinvalidation_unittests, check_deps,
chromeos_unittests, content_browsertests, content_unittests, crypto_unittests,
dbus_unittests, device_unittests, gpu_unittests, interactive_ui_tests,
ipc_tests, jingle_unittests, media_unittests, net_unittests, ppapi_unittests,
printing_unittests, sandbox_linux_unittests, sql_unittests, sync_unit_tests,
unit_tests

[commit-bot: I haz the power, 2012-12-12 17:06:43]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/11543002/1

[commit-bot: I haz the power, 2012-12-12 19:34:39]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[commit-bot: I haz the power, 2012-12-12 19:42:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/11543002/1

[commit-bot: I haz the power, 2012-12-12 19:45:18]

Change committed as 172642