cc: Added tile bundles

This patch adds TileBundles to cc. Currently, in impl
side painting we work with Tiles. A PictureLayerTiling
creates enough tiles to cover its rect (and registers
them with the tile manager), then it updates the
priorities of each of the tile, and finally informs
TileManager to do its work. TileManager sorts and assigns
memory to tiles, and begins rasterization.

With TileBundles, the tiling creates TileBundles (initially
2x2 tiles) to contain tiles. Update tile priorities now
only happens on a per bundle basis. In the initial patch,
TileManager still pulls out each individual tile for
processing.

**** Note to Perf Sheriffs ****
This patch affects performance of several of cc_perftests:
- PictureLayerTilingPerfTest.Invalidate
   This test is expected to regress slightly, but not
   too much.
- PictureLayerTilingPerfTest.UpdateTilePriorities
   This test's performance should improve greatly.
- TileManagerPerfTest.ManageTiles
   This test _should_ remain roughly the same, but there
   might be some up or down as the result of the patch.

Review URL: https://codereview.chromium.org/62283012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239074 0039d316-1c4b-4281-b951-d872f2087c98

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