Add SK_SUPPORT_LEGACY_PORTER_DUFF macro.

include/effects/SkPorterDuff.h

 /*
  * Copyright 2006 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 SkPorterDuff_DEFINED
 #define SkPorterDuff_DEFINED
 
 #include "SkColor.h"
 #include "SkXfermode.h"
 
+//#define SK_SUPPORT_LEGACY_PORTER_DUFF
+
+// Temporary guard until we can remove the dependencies in android. Then we
+// plan to remove this entirely.
+#ifdef SK_SUPPORT_LEGACY_PORTER_DUFF
+
 class SkXfermode;
 
 class SK_API SkPorterDuff {
 public:
     /** List of predefined xfermodes. In general, the algebra for the modes
         uses the following symbols:
         Sa, Sc  - source alpha and color
         Da, Dc - destination alpha and color (before compositing)
         [a, c] - Resulting (alpha, color) values
         For these equations, the colors are in premultiplied state.
@@ skipping 46 matching lines @@
         return false and ignore the mode parameter.
     */
     static bool IsMode(SkXfermode*, Mode* mode);
 
     /** Return the corersponding SkXfermode::Mode
      */
     static SkXfermode::Mode ToXfermodeMode(Mode);
 } SK_ATTR_DEPRECATED("use SkXfermode::Mode");
 
 #endif
+
+#endif