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Since the width is given in pixels which is correct
only on the display with the same DSF, the width needs to
be multiplied by phanton window scale / source scale.

BUG=861967
TEST=Manual. See bug for repro step.

Change-Id: Ib073bb705d8998cf07f41f9d646f0c23828b48de
Reviewed-on: https://chromium-review.googlesource.com/1130595Reviewed-by: Jun Mukai <mukai@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573550}