Add lock back to SharedRendererState

aw: Add lock back to SharedRendererState

It is true that kModeDraw will be called with UI blocked. But it is
possible for kModeProcess to be called asynchronously. We don't access
the state object in kModeProcess, but better be safe than sorry.

BUG=
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=267072

[boliu, 2014-04-28 22:44:00]

hush for review, sgurun for stamp

[sgurun-gerrit only, 2014-04-29 01:24:44]

On 2014/04/28 22:44:00, boliu wrote:
> hush for review, sgurun for stamp

lgtm

[hush (inactive), 2014-04-29 17:38:48]

lgtm

[boliu, 2014-04-29 17:44:05]

The CQ bit was checked by boliu@chromium.org

[commit-bot: I haz the power, 2014-04-29 17:44:59]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/boliu@chromium.org/260213002/40001

[commit-bot: I haz the power, 2014-04-30 04:43:49]

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

[commit-bot: I haz the power, 2014-04-30 04:43:49]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel on tryserver.chromium

[boliu, 2014-04-30 04:45:17]

The CQ bit was checked by boliu@chromium.org

[commit-bot: I haz the power, 2014-04-30 04:45:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/boliu@chromium.org/260213002/40001

[commit-bot: I haz the power, 2014-04-30 05:01:10]

Change committed as 267072