cc: Don't use partial updates for scrollbars when they are not allowed.

Scrollbars always use partial updates, without claiming a partial update
slot from the LayerTreeHost, unlike content layers. However, when partial
updates are not allowed at all (under ubercomp), then the Scrollbar layer
should not do partial updates at all.

Tests:
LayerTreeHostTestAtomicCommit.runMultiThread
LayerTreeHostTestAtomicCommitWithPartialUpdate.runMultiThread

NOTRY=true
BUG=123444
Depends on: https://codereview.chromium.org/11609002

Review URL: https://chromiumcodereview.appspot.com/11464041

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@174503 0039d316-1c4b-4281-b951-d872f2087c98
11 files changed