We're deprecating SkDevice usage in Chromium; this change should

isolate it to skia/ext/ for simpler refactoring.

I took the opportunity to also change calls to the deprecated
SkCanvas::getDeviceSize() to the preferred replacement,
SkCanvas::getBaseLayerSize().

R=fmalita@chromium.org,junov@chromium.org
BUG=543755
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1432443004

Cr-Commit-Position: refs/heads/master@{#361196}