Add the method isOpaque() to SkImage

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 30 matching lines @@
     static SkImage* NewRasterData(const Info&, SkData* pixels, size_t rowBytes);
     static SkImage* NewEncodedData(SkData*);
 
     /**
      * GrTexture is a more logical parameter for this factory, but its
      * interactions with scratch cache still has issues, so for now we take
      * SkBitmap instead. This will be changed in the future. skbug.com/1449
      */
     static SkImage* NewTexture(const SkBitmap&);
 
+    virtual bool isOpaque() const { return false; }
+
     /**
      *  Construct a new SkImage based on the given ImageGenerator.
      *  This function will always take ownership of the passed
      *  ImageGenerator.  Returns NULL on error.
      */
     static SkImage* NewFromGenerator(SkImageGenerator*);
 
     int width() const { return fWidth; }
     int height() const { return fHeight; }
     uint32_t uniqueID() const { return fUniqueID; }
@@ skipping 78 matching lines @@
      *  On failure, false will be returned, and bitmap will unmodified.
      */
     // On ice for now:
     // - should it respect the particular colortype/alphatype of the src
     // - should it have separate entrypoints for preallocated and not bitmaps?
     // - isn't it enough to allow the caller to draw() the image into a canvas?
     bool readPixels(SkBitmap* bitmap, const SkIRect* subset = NULL) const;
 };
 
 #endif