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This allows use of the gtest test generator and easy swarming.

https://codereview.chromium.org/1915003004/ is the build-side change.
https://chromereviews.googleplex.com/411237013/ is the build_internal-side change.

BUG=525873

Review URL: https://codereview.chromium.org/1918733002

Cr-Commit-Position: refs/heads/master@{#389886}