Split DCLayerOverlayProcessor::Process into three functions.

The new functions process individual quads into overlays or underlays.
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2931833005
Cr-Commit-Position: refs/heads/master@{#478765}
2 files changed