View accessibility bounds should be in pixels, not DIPs

The bounding box highlighted by assistive technology
like ZoomText is wrong if the display resolution is not
set to 100%.

BUG=812892,820298

Change-Id: Id488583666c5e01e7aaed5ade7a5a3faeff900cd
Reviewed-on: https://chromium-review.googlesource.com/955545


Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542202}