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This patch re-adds some of the code that was removed during Chrome
Home cleanup to correctly position the overflow menu when anchored to
the bottom of the screen (removal patch fround here:
https://chromium-review.googlesource.com/c/chromium/src/+/934978).

Bug: 866265
Change-Id: I4e4341b138cd9315f9a7fae8cbf47487923a0086
Reviewed-on: https://chromium-review.googlesource.com/1161174Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580300}