Updates nvpr text blobs to not store a direct reference to the
per-glyph GPU path object, but rather store a key for looking it up in
the resource cache. This allows the cache to purge glyphs when needed.
Also indirectly fixes a memory leak that was introduced with nvpr text
blobs.

BUG=skia:

Review URL: https://codereview.chromium.org/1374853004
10 files changed