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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.

Original CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1912621

Fixes:
Change to pak_util.py (PS1 -> PS2) to potentially fix output timestamp

Bug: 1017864
Change-Id: I3bc36777cadfbb8f5a49609b158827c83a4c5bcf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1919559Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715825}