Use scratch keys for stencil buffers.

src/gpu/GrStencilBuffer.h

Index: src/gpu/GrStencilBuffer.h
diff --git a/src/gpu/GrStencilBuffer.h b/src/gpu/GrStencilBuffer.h
index 86fef50225b4cbac3f7c274961ba333d03294be4..187556bd4cffc654e86390f8a95f6411e9060576 100644
--- a/src/gpu/GrStencilBuffer.h
+++ b/src/gpu/GrStencilBuffer.h
@@ -47,9 +47,6 @@ public:
                !fLastClipStackRect.contains(clipSpaceRect);
     }
 
-    // Places the sb in the cache. The cache takes a ref of the stencil buffer.
-    void transferToCache();
-
     static GrResourceKey ComputeKey(int width, int height, int sampleCnt);
 
 protected:
@@ -60,6 +57,7 @@ protected:
         , fBits(bits)
         , fSampleCnt(sampleCnt)
         , fLastClipStackGenID(SkClipStack::kInvalidGenID) {
+        this->setScratchKey(ComputeKey(width, height, sampleCnt));
         fLastClipStackRect.setEmpty();
     }