Start to propagate constness of GrPipelineBuilder up the stack

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index 0ce6bea4e63ea813db3ae41c7e2d0054d92e19c1..b8bec3a6096cccf635d48eeca2cc443024d67904 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -245,7 +245,7 @@ public:
      * 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.
      */
-    virtual bool initCopySurfaceDstDesc(const GrSurface* src, GrSurfaceDesc* desc) = 0;
+    virtual bool initCopySurfaceDstDesc(const GrSurface* 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.