Add some copy support for vulkan msaa

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index 393df1a9b650a4bccd2ac2718a65a0c6ddefb179..3e3a4cd676b0388ef72b41def0fc3f7d6f5e0256 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -308,12 +308,12 @@ public:
                         size_t offset, size_t rowBytes);
 
     /**
-     * This is can be called before allocating a texture to be a dst for copySurface. It will
+     * This is can be called before allocating a texture to be a dst for copySurface. This is only
+     * used for doing dst copies needed in blends, thus the src is always a GrRenderTarget. It will
      * populate the origin, config, and flags fields of the desc such that copySurface can
-     * efficiently succeed. It should only succeed if it can allow copySurface to perform a copy
-     * that would be more effecient than drawing the src to a dst render target.
+     * efficiently succeed.
      */
-    virtual bool initCopySurfaceDstDesc(const GrSurface* src, GrSurfaceDesc* desc) const = 0;
+    virtual bool initDescForDstCopy(const GrRenderTarget* src, GrSurfaceDesc* desc) const = 0;
 
     // After the client interacts directly with the 3D context state the GrGpu
     // must resync its internal state and assumptions about 3D context state.