These functions operate on PaintCanvas and so move them to cc so that
they can continue to work when PaintCanvas is not an SkCanvas.

Additionally, remove skia::GetMetaData which only served to const cast a
pointer that was never const in the first place.  As the underlying
SkCanvas::getMetaData isn't const, this unconstifies the call chains.

BUG=671433
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2686033005
Cr-Commit-Position: refs/heads/master@{#451073}