Skia: Introduce caching of unscaled Bitmaps.

This allows skia to choose whether to use the prescaled bitmap or the
unscaled bitmap depending on which would be optimal in the current
situation. This commit also introduces two functions necessary for
properly resizing Rects when using the non-pre-scaled bitmaps.

CRs-fixed: 451681

Change-Id: I36779d8a680a3ced7c28da492e879de02c7e87a5
Merge remote-tracking branch 'upstream/jb-mr1' into jb-mr1