Record UMA metrics to track content area sizes

Reocrd content area sizes when a new browser window is opened and when
the user resizes a browser window.

This is part of preliminary metrics collection for vision-based
phishing protection.

Bug: 882942
Change-Id: Ib6db98bf13193784b89029f467906ed4e0b3ffc4
Reviewed-on: https://chromium-review.googlesource.com/1228957
Commit-Queue: Jialiu Lin <jialiul@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594031}
8 files changed