GitLab

A child surface ID is either a dependency (something the parents wants
to block its CompositorFrame on and may not exist in the display
compositor yet) or a reference (it is known to exist in the display
compositor).

Dependencies are held in CompositorFrameMetadata::embedded_surfaces, and
references are held in CompositorFrameMetadata::referenced_surfaces.

It was possible for a surface ID to end up in both places if the
primary and fallback SurfaceInfos in a SurfaceLayer matched. This
causes issues in an upcoming CL https://codereview.chromium.org/2831213004/
that "closes" an old fallback surface to receiving new CompositorFrames
if a new primary surface is being requested by a parent to reduce latency.

BUG=672962, 711948
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2861593002
Cr-Commit-Position: refs/heads/master@{#469482}