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Adding estimated memory usage to the quick history provider.
it is suspected to be slow and cause jank on UI thread when memory usage
is high.

These metrics will be received with slow-reports and will help to
investigate some jank on UI thread.

R=mpearson@chromium.org

Bug: 868419
Change-Id: I344f84ec00f318fdb9db63c5b464b119a9d5e3eb
Reviewed-on: https://chromium-review.googlesource.com/1156847
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579919}