add optional SkAlphaType parameter to notifyPixelsChanged

include/core/SkPixelRef.h

Index: include/core/SkPixelRef.h
diff --git a/include/core/SkPixelRef.h b/include/core/SkPixelRef.h
index e65f4a04c5b5e1538c291e69ff1d1d920130f82f..84acd1e7989b7e6eefa86e9d0b33faf350a44f8f 100644
--- a/include/core/SkPixelRef.h
+++ b/include/core/SkPixelRef.h
@@ -1,4 +1,3 @@
-
 /*
  * Copyright 2008 The Android Open Source Project
  *
@@ -6,7 +5,6 @@
  * found in the LICENSE file.
  */
 
-
 #ifndef SkPixelRef_DEFINED
 #define SkPixelRef_DEFINED
 
@@ -134,6 +132,15 @@ public:
     */
     void notifyPixelsChanged();
 
+    /**
+     *  Call if the pixels have changed such that they need a new alphaType.
+     *  e.g. Now the pixels are all opaque (or are no longer all opaque).
+     *
+     *  Calling this, if the specified alphatype difference from the current
+     *  type, will automatically invalidate the generationID.
+     */
+    void notifyAlphaTypeChanged(SkAlphaType);
+
     /** 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.
     */