GitLab

Add a DCHECK to enforce that FrameSinkIds are registered before adding
them to hierarchy. This is already the case for all usage, except one
test which I fixed, but this will enforce it doesn't get broken.

Also remove ImageTransportFactory initialization from
OffscreenCanvasProviderImplTests. It's not actually used.

Bug: 657959
Change-Id: Ie197b655ecb1b1eabb5da56ca92fd590e2dfa450
Reviewed-on: https://chromium-review.googlesource.com/738284Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512508}