Add explicit clear of stencil buffer before opLists that use them

Change-Id: I9e2468e1331c6593dbc6da3ad510f08d1c589e8d
Reviewed-on: https://skia-review.googlesource.com/32041
Commit-Queue: Stan Iliev <stani@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
19 files changed