Refactor client visibility handling

Currently, ContextSupport::SetClientVisibile relies on the caller
remembering to pair visible/not-visible calls. Failure to do so will
result in a "leak", where the context support will always think there
are visible clients.

To avoid this, visibility handling now uses ScopedVisibility objects
which will dcheck if visible > not visible updates are not paired.

This change also introduces a new ContextCacheController object which
handles trimming context caches based on visibility. This simplifies
handling in clients of the ContextProvider and removes this logic
from ContextSupport.

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2278283003
Cr-Commit-Position: refs/heads/master@{#415491}

• android_webview/browser/aw_render_thread_context_provider.cc[diff]
• android_webview/browser/aw_render_thread_context_provider.h[diff]
• blimp/client/support/compositor/blimp_context_provider.cc[diff]
• blimp/client/support/compositor/blimp_context_provider.h[diff]
• cc/BUILD.gn[diff]
• cc/output/context_cache_controller.cc[Added - diff]
• cc/output/context_cache_controller.h[Added - diff]
• cc/output/context_cache_controller_unittest.cc[Added - diff]
• cc/output/context_provider.h[diff]
• cc/output/gl_renderer.cc[diff]
• cc/output/gl_renderer.h[diff]
• cc/output/gl_renderer_unittest.cc[diff]
• cc/raster/raster_buffer_provider_perftest.cc[diff]
• cc/test/test_context_provider.cc[diff]
• cc/test/test_context_provider.h[diff]
• cc/test/test_context_support.cc[diff]
• cc/test/test_context_support.h[diff]
• cc/test/test_in_process_context_provider.cc[diff]
• cc/test/test_in_process_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_unittest.cc[diff]
• content/common/gpu/client/context_provider_command_buffer.cc[diff]
• content/common/gpu/client/context_provider_command_buffer.h[diff]
• gpu/command_buffer/client/context_support.h[diff]
• gpu/command_buffer/client/gles2_implementation.cc[diff]
• gpu/command_buffer/client/gles2_implementation.h[diff]
• gpu/command_buffer/client/gles2_implementation_unittest.cc[diff]
• services/ui/public/cpp/context_provider.cc[diff]
• services/ui/public/cpp/context_provider.h[diff]
• services/ui/surfaces/surfaces_context_provider.cc[diff]
• services/ui/surfaces/surfaces_context_provider.h[diff]
• ui/compositor/test/in_process_context_provider.cc[diff]
• ui/compositor/test/in_process_context_provider.h[diff]