Replace GrExtractAlphaFragmentProcessor with DstIn compose processor

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"
-
-class GLExtractAlphaFragmentProcessor : public GrGLFragmentProcessor {
-public:
-    GLExtractAlphaFragmentProcessor() {}
-
-    void emitCode(EmitArgs& args) override {
-        if (args.fInputColor) {
-            GrGLFragmentBuilder* fsBuilder = args.fBuilder->getFragmentShaderBuilder();
-            fsBuilder->codeAppendf("vec4 alpha4 = %s.aaaa;", args.fInputColor);
-            this->emitChild(0, "alpha4", args.fOutputColor, args);
-        } else {
-            this->emitChild(0, nullptr, args.fOutputColor, args);
-        }
-    }
-
-private:
-    typedef GrGLFragmentProcessor INHERITED;
-};
-
-GrGLFragmentProcessor* GrExtractAlphaFragmentProcessor::onCreateGLInstance() const {
-    return SkNEW(GLExtractAlphaFragmentProcessor);
-}
-
-void GrExtractAlphaFragmentProcessor::onGetGLProcessorKey(const GrGLSLCaps&,
-                                                          GrProcessorKeyBuilder*) const {
-}
-
-bool GrExtractAlphaFragmentProcessor::onIsEqual(const GrFragmentProcessor&) const { return true; }
-
-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));
-}