mus: Get GpuMemoryBuffer from gpu process when possible.

From the window server (i.e. gpu-host process), try to create the
GpuMemoryBuffer from the gpu process first, before falling back
to using shared memory. To do this correctly, it is necessary to
associate these memory buffers to unique client-id of each client.
So create a separate mojom::GpuService instance for each client
(instead of using the same instance for handling requests from all
clients).

BUG=643746
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2503113002
Cr-Commit-Position: refs/heads/master@{#436874}
4 files changed