Use child processors to implement compose color filter.

include/effects/SkModeColorFilter.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkModeColorFilter_DEFINED
 #define SkModeColorFilter_DEFINED
 
@@ skipping 21 matching lines @@
 #ifndef SK_IGNORE_TO_STRING
     void toString(SkString* str) const override {
         str->append("SkModeColorFilter: color: 0x");
         str->appendHex(fColor);
         str->append(" mode: ");
         str->append(SkXfermode::ModeName(fMode));
     }
 #endif
 
 #if SK_SUPPORT_GPU
-    bool asFragmentProcessors(GrContext*, GrProcessorDataManager*,
-                              SkTDArray<const GrFragmentProcessor*>*) const override;
+    const GrFragmentProcessor* asFragmentProcessor(GrContext*,
+                                                   GrProcessorDataManager*) const override;
 #endif
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkModeColorFilter)
 
 protected:
     void flatten(SkWriteBuffer&) const override;
 
 private:
     SkColor             fColor;
     SkXfermode::Mode    fMode;
     // cache
     SkPMColor           fPMColor;
     SkXfermodeProc      fProc;
 
     void updateCache();
 
     typedef SkColorFilter INHERITED;
 };
 
 #endif