Replace GrExtractAlphaFragmentProcessor with DstIn compose processor

gm/dcshader.cpp

Index: gm/dcshader.cpp
diff --git a/gm/dcshader.cpp b/gm/dcshader.cpp
index 56265f16c9513ba3ffae361fa5e9f779191cd77b..09c8af175e32d35f41a535dbfc630f480e85f184 100644
--- a/gm/dcshader.cpp
+++ b/gm/dcshader.cpp
@@ -10,7 +10,7 @@
 #if SK_SUPPORT_GPU
 #include "GrFragmentProcessor.h"
 #include "GrCoordTransform.h"
-#include "effects/GrExtractAlphaFragmentProcessor.h"
+#include "effects/GrXfermodeFragmentProcessor.h"
 #include "gl/GrGLProcessor.h"
 #include "gl/builders/GrGLProgramBuilder.h"
 #include "Resources.h"
@@ -104,7 +104,7 @@ const GrFragmentProcessor* DCShader::asFragmentProcessor(
                                                  SkFilterQuality,
                                                  GrProcessorDataManager* procDataManager) const {
     SkAutoTUnref<const GrFragmentProcessor> inner(new DCFP(procDataManager, fDeviceMatrix));
-    return GrExtractAlphaFragmentProcessor::Create(inner);
+    return MulFragmentProcesorOuputByInputAlpha(inner);
 }
 
 class DCShaderGM : public GM {