[CompositeAfterPaint] Don't paint main frame color overlay twice

This fixes crashes (due to duplicated DrawingDisplayItem ids) of overlay
layout tests in CompositeAfterPaint mode.

Sample errors: https://test-results.appspot.com/data/layout_results/linux_layout_tests_composite_after_paint/761/webkit_layout_tests%20%28with%20patch%29/layout-test-results/results.html

Test: compositing/visibility/overlays*.html in CompositeAfterPaint mode.

Bug: 524134
Change-Id: I206e191bd01768388f1192846d7370abe5f652ed
Reviewed-on: https://chromium-review.googlesource.com/c/1440524
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626909}
1 file changed