The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/32998680778ff8071eb3dd6f8f91a02c046acbc6

commit 32998680778ff8071eb3dd6f8f91a02c046acbc6
Author: Xida Chen <xidachen@chromium.org>
Date: Wed Aug 16 21:21:01 2017

Add UMA to measure memory usage when prepare tiles

This CL adds a histograms to record how much GPU memory do we use when
tile manager assigns memory to tiles. The histogram will tell us
what is the optimal memory limit for low-end android devices with physical
memory of 512MB.

Bug:  754343 
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I49e03b04c41a6a505b7937a617e75664336d7887
Reviewed-on: https://chromium-review.googlesource.com/612183
Reviewed-by: Eric Karl <ericrk@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494953}
[modify] https://crrev.com/32998680778ff8071eb3dd6f8f91a02c046acbc6/cc/tiles/tile_manager.cc
[modify] https://crrev.com/32998680778ff8071eb3dd6f8f91a02c046acbc6/tools/metrics/histograms/histograms.xml