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Currently, the command line switch "--show-dc-layer-debug-borders"
shows borders for only one overlay. This CL extends the support for
multiple overlays on Windows.

Bug: 1117235
Change-Id: I4ba74a24fa402b5b89411e5c079672f6b9bfbcc9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2405559
Commit-Queue: Maggie Chen <magchen@chromium.org>
Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806240}