Remove canvas::NewRaster, and rename surface::NewRasterPMColor to N32Premul

patch from issue 781403002 at patchset 20001 (http://crrev.com/781403002#ps20001)

BUG=skia:
TBR=
re-landing after chrome fixes have landed

Review URL: https://codereview.chromium.org/784223007
15 files changed