Delay activation/draw on GPU tile work completion

Design doc: https://goo.gl/Ku9VBh

This change delays the activation of the pending tree as well as
drawing of active tree tiles on the completion of the required GL
work in the GPU process. This differs from our current
approach, where we only delay activation/draw on the issuing of GL
commands in the renderer, not on the commands being executed in the
GL process.

Note that this behavior is only added in cases where we've enabled the
async worker context via flags.

BUG=673434
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2555743004
Cr-Commit-Position: refs/heads/master@{#447346}

• cc/raster/bitmap_raster_buffer_provider.cc[diff]
• cc/raster/bitmap_raster_buffer_provider.h[diff]
• cc/raster/gpu_raster_buffer_provider.cc[diff]
• cc/raster/gpu_raster_buffer_provider.h[diff]
• cc/raster/one_copy_raster_buffer_provider.cc[diff]
• cc/raster/one_copy_raster_buffer_provider.h[diff]
• cc/raster/raster_buffer_provider.h[diff]
• cc/raster/raster_buffer_provider_unittest.cc[diff]
• cc/raster/zero_copy_raster_buffer_provider.cc[diff]
• cc/raster/zero_copy_raster_buffer_provider.h[diff]
• cc/resources/resource_provider.cc[diff]
• cc/resources/resource_provider.h[diff]
• cc/resources/resource_provider_unittest.cc[diff]
• cc/test/fake_raster_buffer_provider.cc[diff]
• cc/test/fake_raster_buffer_provider.h[diff]
• cc/tiles/picture_layer_tiling.h[diff]
• cc/tiles/tile_draw_info.cc[diff]
• cc/tiles/tile_draw_info.h[diff]
• cc/tiles/tile_manager.cc[diff]
• cc/tiles/tile_manager.h[diff]
• cc/tiles/tile_manager_unittest.cc[diff]