Minor changes to GrFontCache system.

The main change is parameterizing the GrAtlasMgr so it can have a different sized backing texture and a different number of plots. This is in support of the saveLayer cache which has a smaller backing texture and only one plot.

R=jvanverth@google.com, bsalomon@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/217423014

git-svn-id: http://skia.googlecode.com/svn/trunk@14011 2bbb7eff-a529-9590-31e7-b0007b416f81
7 files changed