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These flags existed in chrome://flags as an escape hatch for users
during testing.

Now that HTML5 by Default has completely launched, they are no longer
needed.

Bug: 709550
Change-Id: I1a140a86581483913681055c246a0c2509d783c2
Reviewed-on: https://chromium-review.googlesource.com/580331
Commit-Queue: Tommy Li <tommycli@chromium.org>
Reviewed-by: Anthony LaForge <laforge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488516}