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..e39c9657aff07590105c3adb045f2ee223a04797 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 initCopySurfaceDstDesc(const GrRenderTarget* src, GrSurfaceDesc* desc) const = 0;

[bsalomon, 2016/08/30 13:07:20]

Is this part of the change incidental or necessary?

[egdaniel, 2016/08/30 13:40:46]

It is not necessary, but it does make some of the code slightly cleaner not
having to check if the src is a RT or not. But in general if we are only using
the function in cases where the src is an RT I feel likes its better to restrict
it and then we can expand it back to Surface if we find a good reason.

[bsalomon, 2016/08/30 15:29:21]

If we're going to narrow the definition of the function to those use cases, can
we rename it to something like "initDescForDstCopy"?

[egdaniel, 2016/08/30 15:45:13]

Done.

 
     // After the client interacts directly with the 3D context state the GrGpu
     // must resync its internal state and assumptions about 3D context state.