add getTextureHandle to SkSurface

include/core/SkSurface.h

Index: include/core/SkSurface.h
diff --git a/include/core/SkSurface.h b/include/core/SkSurface.h
index 8ccfa311245bcf7bc63e9f5aabb8f6124c892317..5d08ee67d30e6302e4a21e365b38ca8e96a366f3 100644
--- a/include/core/SkSurface.h
+++ b/include/core/SkSurface.h
@@ -138,9 +138,25 @@ public:
     /**
      *  Call this if the contents are about to change. This will (lazily) force a new
      *  value to be returned from generationID() when it is called next.
+     *
+     *  CAN WE DEPRECATE THIS?
      */
     void notifyContentWillChange(ContentChangeMode mode);
 
+    enum TextureHandleAccess {
+        kFlushRead_TextureHandleAccess,     //!< caller may read from the texture
+        kFlushWrite_TextureHandleAccess,    //!< caller may write to the texture
+        kDiscardWrite_TextureHandleAccess,  //!< caller must over-write the entire texture
+    };
+    /**
+     *  Retrieves the backend API handle of the texture used by this surface, or 0 if the surface
+     *  is not backed by a GPU texture.
+     *
+     *  The returned texture-handle is only valid until the next draw-call into the surface,
+     *  or the surface is deleted.
+     */
+    GrBackendObject getTextureHandle(TextureHandleAccess);
+
     /**
      *  Return a canvas that will draw into this surface. This will always
      *  return the same canvas for a given surface, and is manged/owned by the