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This allows downstream embedders to specify their own branding files
and locations without having to patch chromium source files.

Change-Id: I8b5c1d71a11998ef68b586f11326d82aced35529
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1932781Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Yngve Pettersen <yngve@vivaldi.com>
Cr-Commit-Position: refs/heads/master@{#721428}