Add helper for creating leaf FPs inside GrFP::TestCreate functions

src/gpu/effects/GrExtractAlphaFragmentProcessor.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "effects/GrExtractAlphaFragmentProcessor.h"
 #include "gl/GrGLFragmentProcessor.h"
 #include "gl/builders/GrGLProgramBuilder.h"
@@ skipping 29 matching lines @@
 void GrExtractAlphaFragmentProcessor::onComputeInvariantOutput(GrInvariantOutput* inout) const {
     if (inout->validFlags() & kA_GrColorComponentFlag) {
         GrColor color = GrColorPackA4(GrColorUnpackA(inout->color()));
         inout->setToOther(kRGBA_GrColorComponentFlags, color,
                           GrInvariantOutput::kWill_ReadInput);
     } else {
         inout->setToUnknown(GrInvariantOutput::kWill_ReadInput);
     }
     this->childProcessor(0).computeInvariantOutput(inout);
 }
+
+GR_DEFINE_FRAGMENT_PROCESSOR_TEST(GrExtractAlphaFragmentProcessor);
+
+const GrFragmentProcessor* GrExtractAlphaFragmentProcessor::TestCreate(GrProcessorTestData* d) {
+    SkAutoTUnref<const GrFragmentProcessor> child(GrProcessorUnitTest::CreateChildFP(d));
+    return SkNEW_ARGS(GrExtractAlphaFragmentProcessor, (child));
+}