Move some of the adding stencil attachment logic of Gpu and into Render Target.

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index ba9e85b54f12924df4a78b85f998b3cdf7f72f6c..58afe4909757b343418dded641279a5ce20eeff0 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -373,8 +373,15 @@ public:
     virtual bool isTestingOnlyBackendTexture(GrBackendObject id) const = 0;
     virtual void deleteTestingOnlyBackendTexture(GrBackendObject id) const = 0;
 
-    // Given a rt, find or create a stencil buffer and attach it
-    bool attachStencilAttachmentToRenderTarget(GrRenderTarget* target);
+    // Given the input GrRenderTarget, this function sets GrStencilAttachment* either
+    // from a cached stencil attachment or by creating a new one. If the GrStencilAttachment*
+    // that is returned is non-null, the caller will own the ref on the GrStencilAttachment.
+    // This function returns true if the returned GrStencilAttachment was newly created in case
+    // the caller wants to do any special thing with the stencil (e.g. clearning it).
+    bool getStencilAttachment(const GrRenderTarget*, GrStencilAttachment**);
+
+    // clears target's entire stencil buffer to 0
+    virtual void clearStencil(GrRenderTarget* target) = 0;
 
     // This is only to be used in GL-specific tests.
     virtual const GrGLContext* glContextForTesting() const { return nullptr; }
@@ -471,15 +478,10 @@ private:
                                const SkIPoint& dstPoint) = 0;
 
     // width and height may be larger than rt (if underlying API allows it).
-    // Should attach the SB to the RT. Returns false if compatible sb could
-    // not be created.
-    virtual bool createStencilAttachmentForRenderTarget(GrRenderTarget*, int width, int height) = 0;
-
-    // attaches an existing SB to an existing RT.
-    virtual bool attachStencilAttachmentToRenderTarget(GrStencilAttachment*, GrRenderTarget*) = 0;
-
-    // clears target's entire stencil buffer to 0
-    virtual void clearStencil(GrRenderTarget* target) = 0;
+    // Returns nullptr if compatible sb could not be created.
+    virtual GrStencilAttachment* createStencilAttachmentForRenderTarget(const GrRenderTarget*,
+                                                                        int width,
+                                                                        int height) = 0;
 
     void resetContext() {
         this->onResetContext(fResetBits);