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

include/core/SkImage.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_DEFINED
 #define SkImage_DEFINED
 
@@ skipping 282 matching lines @@
 
     /**
      *  Return a new image that is a subset of this image. The underlying implementation may
      *  share the pixels, or it may make a copy.
      *
      *  If subset does not intersect the bounds of this image, or the copy/share cannot be made,
      *  NULL will be returned.
      */
     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 {
         kRO_LegacyBitmapMode,
         kRW_LegacyBitmapMode,
     };
 
     /**
      *  Attempt to create a bitmap with the same pixels as the image. The result will always be
      *  a raster-backed bitmap (texture-backed bitmaps are DEPRECATED, and not supported here).
@@ skipping 16 matching lines @@
 
 private:
     const int       fWidth;
     const int       fHeight;
     const uint32_t  fUniqueID;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif