Avoid repeat call to set number of worker threads in Single Process

Avoid repeat call to set number of worker threads in Single Process

In single process mode with impl-side-painting, browser and renderer
would both try to set number of raster worker threads, which causes
DCHECK. This CL makes sure there won't be duplicate call to set number
of worker threads in single process mode.

R=enne
BUG=314185
Committed: https://crrev.com/67c3b8b09ef08fcbc2f22c75c39b68f1df9610b9
Cr-Commit-Position: refs/heads/master@{#318995}

[enne (OOO), 2015-03-02 22:45:49]

lgtm, but I'm not an owner.

[weiliangc, 2015-03-02 22:53:19]

weiliangc@chromium.org changed reviewers:
+ piman@chromium.org

[weiliangc, 2015-03-02 22:54:20]

piman@?

[piman, 2015-03-04 00:38:37]

lgtm

[weiliangc, 2015-03-04 00:54:43]

The CQ bit was checked by weiliangc@chromium.org

[commit-bot: I haz the power, 2015-03-04 00:56:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/971943002/1

[commit-bot: I haz the power, 2015-03-04 02:02:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-04 02:03:02]

Patchset 1 (id:??) landed as
https://crrev.com/67c3b8b09ef08fcbc2f22c75c39b68f1df9610b9
Cr-Commit-Position: refs/heads/master@{#318995}