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This CL adds support for compressing .pak files, and adds compression
for locales/*.pak on chromeos.

Note: We keep the extension for compressed .pak files to avoid
dependency complexity in tests.

Bug: 1017864
Change-Id: Ifee472b7e15673fcb835ae75aca768265592460b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1912621
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715173}