GitLab

This CL contains:
 - Convert MIDIOutput::pending_data_ to contain DOMUint8Array instead of
   Vector, so that we don't need an extra copy on the lazy open case.
 - Take care null or non-Document ExecutionContext.
 - Misc clean up.

Change-Id: I33862de0aa39ddd68dc9ee5e4a594caf1e8f7437
Reviewed-on: https://chromium-review.googlesource.com/895129
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533254}