Replace GrExtractAlphaFragmentProcessor with DstIn compose processor

src/gpu/GrProcessor.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrProcessor.h"
 #include "GrContext.h"
 #include "GrCoordTransform.h"
@@ skipping 223 matching lines @@
     }
     int count = this->numTransforms();
     for (int i = 0; i < count; ++i) {
         if (this->coordTransform(i) != that.coordTransform(i)) {
             return false;
         }
     }
     return true;
 }
 
+#include "effects/GrXfermodeFragmentProcessor.h"
+
+const GrFragmentProcessor* GrFragmentProcessor::MulOuputByInputAlpha(
+    const GrFragmentProcessor* fp) {
+    return GrXfermodeFragmentProcessor::CreateFromDstProcessor(fp, SkXfermode::kDstIn_Mode);
+}
+
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 // Initial static variable from GrXPFactory
 int32_t GrXPFactory::gCurrXPFClassID =
         GrXPFactory::kIllegalXPFClassID;