cc: Fix RasterWorkerPool shutdown crash.

Avoid calling sort on the raster thread vector while deleting its
elements. This also adds a "IsRunning" state that is used to
check that that the worker pool is not used incorrectly during
shutdown.

BUG=172059
R=nduca@chromium.org
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/12079028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@179321 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed