Add host type check for blink::WebGLRenderingContextBase::commit

WebGLRenderingContextBase::commit early out if the host type is not
OffscreenCanvas.

Bug: 976830
Change-Id: If64fc5e38177f9ba80ca33985d8db476c3ed0179
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1696273
Commit-Queue: Yi Xu <yiyix@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#677872}
5 files changed