cc: Rename DirectRasterWorkerPool to GpuRasterWorkerPool

This renames DirectRasterWorkerPool to GpuRasterWorkerPool 
to make it obvious that TileManager uses Gpu rasterization, 
and also limits the usage of this implementation to gpu raster.

BUG=389447

Review URL: https://codereview.chromium.org/328263005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@280789 0039d316-1c4b-4281-b951-d872f2087c98
9 files changed