cc: Apply contents scales to impl-side painting rasterization

Tiles now have a contents scale that they are rastered with, so that non-1.0
contents scales work.  Additionally, PictureLayer derives from
ContentsScalingLayer so that it picks up the right content bounds and default
contents scale.

BUG=155209


Review URL: https://chromiumcodereview.appspot.com/11421210

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171111 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed