Add CPU backing store for GrAtlas to reduce texture uploads.
This change creates a temporary copy of each GrPlot on the CPU
side. As we add glyphs to a plot, a dirty rectangle is tracked,
and just before we render text we upload all of the dirty areas
to the atlas texture. Once a plot is nearly full, we assume that
we may only be adding one or two glyphs before rendering, so we
delete the CPU backing memory to save space, and upload directly.
BUG=366225
R=robertphillips@google.com
Author: jvanverth@google.com
Review URL: https://codereview.chromium.org/269423007
git-svn-id: http://skia.googlecode.com/svn/trunk@14729 2bbb7eff-a529-9590-31e7-b0007b416f81
8 files changed