cc:: Add remote mode to the compositor.

- Added RemoteChannelMain and RemoteChannelImpl to serialize and transmit
  inter-proxy messages between the main and impl components of the
  compositor using protobufs.
- Added RemoteChannelHost to be used by the cc embedder as the API for
  interacting with the impl components of the remote compositor.
- Added tests to verify the initialization and shutdown sequence for the
  remote compositor.

BUG=550687
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1513643010

Cr-Commit-Position: refs/heads/master@{#372236}

• cc/BUILD.gn[diff]
• cc/cc.gyp[diff]
• cc/cc_tests.gyp[diff]
• cc/layers/layer_unittest.cc[diff]
• cc/layers/scrollbar_layer_unittest.cc[diff]
• cc/layers/texture_layer_unittest.cc[diff]
• cc/proto/BUILD.gn[diff]
• cc/proto/compositor_message.proto[diff]
• cc/proto/compositor_message_to_impl.proto[Added - diff]
• cc/proto/compositor_message_to_main.proto[Added - diff]
• cc/test/fake_layer_tree_host.cc[diff]
• cc/test/layer_tree_pixel_test.cc[diff]
• cc/test/layer_tree_test.cc[diff]
• cc/test/layer_tree_test.h[diff]
• cc/test/proxy_main_for_test.cc[diff]
• cc/test/proxy_main_for_test.h[diff]
• cc/test/remote_channel_impl_for_test.cc[Added - diff]
• cc/test/remote_channel_impl_for_test.h[Added - diff]
• cc/test/remote_proto_channel_bridge.cc[Added - diff]
• cc/test/remote_proto_channel_bridge.h[Added - diff]
• cc/test/test_hooks.h[diff]
• cc/test/threaded_channel_for_test.cc[diff]
• cc/test/threaded_channel_for_test.h[diff]
• cc/trees/compositor_mode.h[diff]
• cc/trees/layer_tree_host.cc[diff]
• cc/trees/layer_tree_host.h[diff]
• cc/trees/layer_tree_host_common_perftest.cc[diff]
• cc/trees/layer_tree_host_perftest.cc[diff]
• cc/trees/layer_tree_host_unittest.cc[diff]
• cc/trees/layer_tree_host_unittest_context.cc[diff]
• cc/trees/layer_tree_host_unittest_copyrequest.cc[diff]
• cc/trees/layer_tree_host_unittest_proxy.cc[diff]
• cc/trees/layer_tree_host_unittest_record_gpu_histogram.cc[diff]
• cc/trees/layer_tree_host_unittest_scroll.cc[diff]
• cc/trees/proxy_impl_unittest.cc[diff]
• cc/trees/proxy_main.cc[diff]
• cc/trees/proxy_main.h[diff]
• cc/trees/remote_channel_impl.cc[Added - diff]
• cc/trees/remote_channel_impl.h[Added - diff]
• cc/trees/remote_channel_main.cc[Added - diff]
• cc/trees/remote_channel_main.h[Added - diff]
• cc/trees/remote_channel_unittest.cc[Added - diff]
• cc/trees/remote_proto_channel.h[diff]
• cc/trees/threaded_channel.cc[diff]
• cc/trees/threaded_channel.h[diff]
• ui/android/resources/resource_manager_impl_unittest.cc[diff]