cc: Add threaded GPU rasterization.

Enable flag: --enable-threaded-gpu-rasterization

This patch enables threaded rasterization in GpuTileTaskWorkerPool.

There are some not yet landed/rolled dependencies:

  InProcessContextProvider Context Lost handling (jbauman@).
  Without this the feature should be considered unstable on WebViews.

BUG=454500

Review URL: https://codereview.chromium.org/916723002

Cr-Commit-Position: refs/heads/master@{#316333}

• cc/layers/picture_layer_impl.cc[diff]
• cc/layers/picture_layer_impl_unittest.cc[diff]
• cc/output/context_provider.h[diff]
• cc/output/output_surface.cc[diff]
• cc/output/output_surface.h[diff]
• cc/output/output_surface_unittest.cc[diff]
• cc/resources/gpu_rasterizer.cc[diff]
• cc/resources/gpu_rasterizer.h[diff]
• cc/resources/gpu_tile_task_worker_pool.cc[diff]
• cc/resources/gpu_tile_task_worker_pool.h[diff]
• cc/resources/resource_provider.cc[diff]
• cc/resources/resource_provider.h[diff]
• cc/resources/resource_provider_unittest.cc[diff]
• cc/resources/tile_task_worker_pool_perftest.cc[diff]
• cc/resources/tile_task_worker_pool_unittest.cc[diff]
• cc/test/failure_output_surface.cc[diff]
• cc/test/fake_output_surface.cc[diff]
• cc/test/fake_output_surface.h[diff]
• cc/test/layer_tree_pixel_resource_test.cc[diff]
• cc/test/layer_tree_pixel_test.cc[diff]
• cc/test/pixel_test.cc[diff]
• cc/test/pixel_test_output_surface.cc[diff]
• cc/test/pixel_test_output_surface.h[diff]
• cc/test/test_context_provider.cc[diff]
• cc/test/test_context_provider.h[diff]
• cc/trees/layer_tree_host_impl.cc[diff]
• cc/trees/layer_tree_host_impl.h[diff]
• cc/trees/layer_tree_host_impl_unittest.cc[diff]
• cc/trees/layer_tree_host_unittest.cc[diff]
• cc/trees/layer_tree_settings.cc[diff]
• cc/trees/layer_tree_settings.h[diff]
• content/browser/android/in_process/synchronous_compositor_factory_impl.cc[diff]
• content/browser/android/in_process/synchronous_compositor_factory_impl.h[diff]
• content/browser/android/in_process/synchronous_compositor_impl.cc[diff]
• content/browser/android/in_process/synchronous_compositor_output_surface.cc[diff]
• content/browser/android/in_process/synchronous_compositor_output_surface.h[diff]
• content/common/gpu/client/context_provider_command_buffer.cc[diff]
• content/common/gpu/client/context_provider_command_buffer.h[diff]
• content/common/gpu/client/gpu_channel_host.cc[diff]
• content/renderer/gpu/render_widget_compositor.cc[diff]
• content/renderer/render_thread_impl.cc[diff]
• content/renderer/render_widget.cc[diff]
• webkit/common/gpu/context_provider_in_process.cc[diff]
• webkit/common/gpu/context_provider_in_process.h[diff]