clipstacks can be on the stack or embedded, therefore should not be ref-counted

BUG=skia:

Change-Id: I7e16034d463a1db1baac404f775cf33076cbbf73
Reviewed-on: https://skia-review.googlesource.com/9509
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed