viz: Convert a sync api in ServerGpuMemoryBufferManager into async.
Convert ServerGpuMemoryBufferManager::CreateGpuMemoryBufferHandle() into
an async api. This is in preparation for using this implementation from
content.
BUG=733482
TBR=jbauman@ for gpu_memory_buffer_manager.h doc update
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;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/2941933002
Cr-Commit-Position: refs/heads/master@{#481517}
10 files changed
