Use child processors to implement compose color filter.

src/effects/SkLumaColorFilter.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkLumaColorFilter.h"
 
 #include "SkColorPriv.h"
@@ skipping 36 matching lines @@
 
 #ifndef SK_IGNORE_TO_STRING
 void SkLumaColorFilter::toString(SkString* str) const {
     str->append("SkLumaColorFilter ");
 }
 #endif
 
 #if SK_SUPPORT_GPU
 class LumaColorFilterEffect : public GrFragmentProcessor {
 public:
-    static GrFragmentProcessor* Create() {
+    static const GrFragmentProcessor* Create() {
         static LumaColorFilterEffect gLumaEffect;
         return SkRef(&gLumaEffect);
     }
 
     const char* name() const override { return "Luminance-to-Alpha"; }
 
     class GLProcessor : public GrGLFragmentProcessor {
     public:
         GLProcessor(const GrProcessor&) {}
 
@@ skipping 33 matching lines @@
 
     bool onIsEqual(const GrFragmentProcessor&) const override { return true; }
 
     void onComputeInvariantOutput(GrInvariantOutput* inout) const override {
         // The output is always black. The alpha value for the color passed in is arbitrary.
         inout->setToOther(kRGB_GrColorComponentFlags, GrColorPackRGBA(0, 0, 0, 0),
                           GrInvariantOutput::kWill_ReadInput);
     }
 };
 
-bool SkLumaColorFilter::asFragmentProcessors(GrContext*, GrProcessorDataManager*,
-                                             SkTDArray<const GrFragmentProcessor*>* array) const {
+const GrFragmentProcessor* SkLumaColorFilter::asFragmentProcessor(GrContext*,
+                                                                  GrProcessorDataManager*) const {
 
-    GrFragmentProcessor* frag = LumaColorFilterEffect::Create();
-    if (frag) {
-        if (array) {
-            *array->append() = frag;
-        } else {
-            frag->unref();
-            SkDEBUGCODE(frag = nullptr;)
-        }
-        return true;
-    }
-    return false;
+    return LumaColorFilterEffect::Create();
 }
 #endif