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

include/gpu/GrRenderTarget.h

Index: include/gpu/GrRenderTarget.h
diff --git a/include/gpu/GrRenderTarget.h b/include/gpu/GrRenderTarget.h
index 8983d53a251847325254441c86492436d555c088..112d8d2a65d7b5ab1e7583705a921e350994859b 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -165,6 +165,12 @@ private:
     // Checked when this object is asked to attach a stencil buffer.
     virtual bool canAttemptStencilAttachment() const = 0;
 
+    // Allows the backends to perform any additional work that is required from attaching a
+    // GrStencilAttachment. When this is called, the GrStencilAttachment has already been put onto
+    // the GrRenderTarget. This function must return false if any failures occur when completing the
+    // stencil attachment.
+    virtual bool completeStencilAttachment() = 0;
+
     friend class GrRenderTargetPriv;
 
     GrStencilAttachment*  fStencilAttachment;