change setAlphaType to not modify the pixelref's genID

include/core/SkPixelRef.h

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPixelRef_DEFINED
 #define SkPixelRef_DEFINED
 
@@ skipping 112 matching lines @@
     /** Returns a non-zero, unique value corresponding to the pixels in this
         pixelref. Each time the pixels are changed (and notifyPixelsChanged is
         called), a different generation ID will be returned.
     */
     uint32_t getGenerationID() const;
 
     /**
      *  Call this if you have changed the contents of the pixels. This will in-
      *  turn cause a different generation ID value to be returned from
      *  getGenerationID().
-     *
-     *  If the alphatype has also changed, specify its new value as well. If
-     *  the new pixels' alphatype is the same, this can be called with no
-     *  parameter.
      */
-    void notifyPixelsChanged(SkAlphaType);
-    void notifyPixelsChanged() {
-        this->notifyPixelsChanged(fInfo.fAlphaType);
-    }
+    void notifyPixelsChanged();
+
+    /**
+     *  Change the info's AlphaType. Note that this does not automatically
+     *  invalidate the generation ID. If the pixel values themselves have
+     *  changed, then you must explicitly call notifyPixelsChanged() as well.
+     */
+    void changeAlphaType(SkAlphaType at);
 
     /** Returns true if this pixelref is marked as immutable, meaning that the
         contents of its pixels will not change for the lifetime of the pixelref.
     */
     bool isImmutable() const { return fIsImmutable; }
 
     /** Marks this pixelref is immutable, meaning that the contents of its
         pixels will not change for the lifetime of the pixelref. This state can
         be set on a pixelref, but it cannot be cleared once it is set.
     */
@@ skipping 224 matching lines @@
     /**
      *  Allocate a new pixelref matching the specified ImageInfo, allocating
      *  the memory for the pixels. If the ImageInfo requires a ColorTable,
      *  the pixelref will ref() the colortable.
      *  On failure return NULL.
      */
     virtual SkPixelRef* create(const SkImageInfo&, SkColorTable*) = 0;
 };
 
 #endif