enable the feature of establish GPU channel asynchronously

[Lowell Liu]

Hi cduvall, we faced an issue  https://issues.chromium.org/issues/345275130,  the render process can not quit after main process quit or crash,  root cause is the render's main thread is busy on handle  RequestNewLayerTreeFrameSink,  if enable the feature of establish GPU channel asynchronously can fix this issue, but we are not sure  what risks will it introduce, could you help to have a response for us?