Remove memory pool use from SkTextBlobCache

Track used size explicitly in the cache enabling DDL to use
the LRU.

Change-Id: I3fef593e9252172dd160fd7636254550b95ca0a2
Reviewed-on: https://skia-review.googlesource.com/130022
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Herb Derby <herb@google.com>
5 files changed