Add native caching of uniquely keyed GrTextureProxies

Change-Id: I303fe025b7856b8d681a2d35b416c015bd468e1d
Reviewed-on: https://skia-review.googlesource.com/48300
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
18 files changed