Allow wrapped resources to have unique keys

Allow wrapped resources to have unique keys

Previously, wrapped resources were never budgeted. Now we explicitly allow
wrapped, unbudgeted resources with unique keys. This allows code that
wraps (and re-wraps) external resources with a deterministic key to find
the same wrapped resource - saving time and ensuring a single wrapped
copy, to preserve state on the resource (like texture sampler state).

Bug: skia:
Change-Id: I1dd7642f1ed8bb6c620029d46203cf5cb6b3c160
Reviewed-on: https://skia-review.googlesource.com/15241
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>