Use scratch keys for stencil buffers.

src/gpu/GrResourceCache2.h

Index: src/gpu/GrResourceCache2.h
diff --git a/src/gpu/GrResourceCache2.h b/src/gpu/GrResourceCache2.h
index 9331e9dfd3f73af46bd9dbdd0b833c9ea3762d5a..3c5eea5a3f42e58308ffcadf92aa75b5cdc0045f 100644
--- a/src/gpu/GrResourceCache2.h
+++ b/src/gpu/GrResourceCache2.h
@@ -161,6 +161,7 @@ private:
     void notifyPurgable(GrGpuResource*);
     void didChangeGpuMemorySize(const GrGpuResource*, size_t oldSize);
     bool didSetContentKey(GrGpuResource*);
+    void willRemoveScratchKey(const GrGpuResource*);
     void didChangeBudgetStatus(GrGpuResource*);
     void makeResourceMRU(GrGpuResource*);
     /// @}
@@ -277,6 +278,12 @@ private:
      */
     bool didSetContentKey(GrGpuResource* resource) { return fCache->didSetContentKey(resource); }
 
+    /**
+     * Called by GrGpuResources when the remove their scratch key.
+     */
+    void willRemoveScratchKey(const GrGpuResource* resource) {
+        fCache->willRemoveScratchKey(resource);
+    }
 
     /**
      * Called by GrGpuResources when they change from budgeted to unbudgeted or vice versa.