exo: fix scale problem in mushrome

In muschrome, exo doesn't render correctly if the device scale factor is
not 1. In exo, surface's size is in dip, but the size of viz::Surface is
in pixel. So we need scale the exo surfaces when we composite them to a
viz::Surface.

Bug: 731742
Change-Id: I4c86e5d53053b36a1889de7afb425aa68017a2b6
Reviewed-on: https://chromium-review.googlesource.com/616841
Commit-Queue: Peng Huang <[email protected]>
Reviewed-by: David Reveman <[email protected]>
Cr-Commit-Position: refs/heads/master@{#499088}
5 files changed