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

src/gpu/effects/GrExtractAlphaFragmentProcessor.cpp

Index: src/gpu/effects/GrExtractAlphaFragmentProcessor.cpp
diff --git a/src/gpu/effects/GrExtractAlphaFragmentProcessor.cpp b/src/gpu/effects/GrExtractAlphaFragmentProcessor.cpp
index 8f6af65ca77be81034ab62d8c8f906f5b107a435..483df645022afb3ebfecb6645f3b48bf44a980ba 100644
--- a/src/gpu/effects/GrExtractAlphaFragmentProcessor.cpp
+++ b/src/gpu/effects/GrExtractAlphaFragmentProcessor.cpp
@@ -47,3 +47,10 @@ void GrExtractAlphaFragmentProcessor::onComputeInvariantOutput(GrInvariantOutput
     }
     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));
+}