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This CL fixes two things: it removes the perf metrics HUD in iframes,
and it stops flashing of metrics in some cases.

R=sadrul

Change-Id: I0b6603600c48bffbe6229a11f8798b0bb6ec31d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2601218Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: weiliangc <weiliangc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839794}