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This makes sure LTHI notifies the Scheduler of all ManageTiles calls
and then avoids a scheduled ManageTiles if we are already averaging
one or more ManageTiles per BeginImplFrame.

Limiting the scheduled ManageTiles to occur only if a ManageTiles
hasn't happened in the current frame can still result in two
ManageTiles per frame since we might schedule a ManageTiles at the
begining of a frame and then call explicitly when the commit finishes
if the main thread is in a high latency mode.

BUG=334749

Review URL: https://codereview.chromium.org/130483010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245388 0039d316-1c4b-4281-b951-d872f2087c98