The TextBlobCache needs the ability to trigger a flush because otherwise its entire budget can be used up, but it will not be able to free up any space due to blobs being stuck in the GrInOrderDrawBuffer.  This was causing a segfault.  After this CL the cache will try to purge, and then flush if it cannot purge enough.  It will not purge the most recent addition to the cache.

TBR=bsalomon@google.com
BUG=skia:

Review URL: https://codereview.chromium.org/1071333002
3 files changed