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..ef0be280b1facbe6e2b5c90f57e98e2a13944066 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -374,7 +374,17 @@ public:
     virtual void deleteTestingOnlyBackendTexture(GrBackendObject id) const = 0;
 
     // Given a rt, find or create a stencil buffer and attach it
-    bool attachStencilAttachmentToRenderTarget(GrRenderTarget* target);
+//    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;

[egdaniel, 2015/09/11 17:59:49]

Since we are not letting the RT handle the attaching, the RT also has to be
responsible for calling clear on the stencil. For future work, maybe this clear
should really be implemented in the RT and not the gpu.

 
     // This is only to be used in GL-specific tests.
     virtual const GrGLContext* glContextForTesting() const { return nullptr; }
@@ -471,15 +481,10 @@ 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);