cc: Generalize raster task notifications

This patch generalizes the way we handle notifications for sets of raster
tasks. Previously, this was special cases for tiles that are required for
activation. The new implementation allows arbitrary sets of task and
notificatios for them, and it makes the rasterizer and the worker pools
agnostic of the semantics of those sets (only the TileManager knows about
this).

R=reveman@chromium.org
BUG=388030

Review URL: https://codereview.chromium.org/523243002

Cr-Commit-Position: refs/heads/master@{#295392}

• cc/resources/gpu_raster_worker_pool.cc[diff]
• cc/resources/gpu_raster_worker_pool.h[diff]
• cc/resources/image_copy_raster_worker_pool.cc[diff]
• cc/resources/image_copy_raster_worker_pool.h[diff]
• cc/resources/image_raster_worker_pool.cc[diff]
• cc/resources/image_raster_worker_pool.h[diff]
• cc/resources/pixel_buffer_raster_worker_pool.cc[diff]
• cc/resources/pixel_buffer_raster_worker_pool.h[diff]
• cc/resources/raster_worker_pool.cc[diff]
• cc/resources/raster_worker_pool.h[diff]
• cc/resources/raster_worker_pool_perftest.cc[diff]
• cc/resources/raster_worker_pool_unittest.cc[diff]
• cc/resources/rasterizer.cc[diff]
• cc/resources/rasterizer.h[diff]
• cc/resources/tile_manager.cc[diff]
• cc/resources/tile_manager.h[diff]
• cc/test/fake_tile_manager.cc[diff]
• cc/test/fake_tile_manager.h[diff]