cc: Partial tile raster for BitmapTileTaskWorkerPool.

For software compositing, this will reuse resources when possible
to avoid rastering the full tile. This improves the time to
raster a single animating tab loading spinner from 0.283474 ms to
0.0729661 ms per frame, for a 74% reduction in raster time.

To reproduce use the --disable-gpu command line flag.

R=reveman, vmpstr
BUG=487387
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1157103006

Cr-Commit-Position: refs/heads/master@{#332257}

• cc/raster/bitmap_tile_task_worker_pool.cc[diff]
• cc/raster/bitmap_tile_task_worker_pool.h[diff]
• cc/raster/gpu_tile_task_worker_pool.cc[diff]
• cc/raster/gpu_tile_task_worker_pool.h[diff]
• cc/raster/one_copy_tile_task_worker_pool.cc[diff]
• cc/raster/one_copy_tile_task_worker_pool.h[diff]
• cc/raster/pixel_buffer_tile_task_worker_pool.cc[diff]
• cc/raster/pixel_buffer_tile_task_worker_pool.h[diff]
• cc/raster/raster_buffer.h[diff]
• cc/raster/tile_task_runner.h[diff]
• cc/raster/tile_task_worker_pool_unittest.cc[diff]
• cc/raster/zero_copy_tile_task_worker_pool.cc[diff]
• cc/raster/zero_copy_tile_task_worker_pool.h[diff]
• cc/test/fake_tile_manager.cc[diff]
• cc/tiles/tile_manager.cc[diff]
• cc/trees/layer_tree_host_pixeltest_tiles.cc[diff]