Add SkImage factory method that forces image to be resolved to a texture.

include/core/SkImage.h

Index: include/core/SkImage.h
diff --git a/include/core/SkImage.h b/include/core/SkImage.h
index 62a9e9cf426bc132ded0e4fad45aa76306361b0f..e60902fc07419acc8fc7006c6c67f773a427a758 100644
--- a/include/core/SkImage.h
+++ b/include/core/SkImage.h
@@ -300,6 +300,13 @@ public:
      */
     SkImage* newSubset(const SkIRect& subset) const;
 
+    /**
+     *  Ensures that an image is backed by a texture (when GrContext is non-null). If no
+     *  transformation is required, the returned image may be the same as this image. If the this
+     *  image is from a different GrContext, this will fail.
+     */
+    SkImage* newTextureImage(GrContext*) const;
+
     // Helper functions to convert to SkBitmap
 
     enum LegacyBitmapMode {