add virtuals to optimize composing colorfilters

include/effects/SkColorMatrixFilter.h

 /*
  * Copyright 2007 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkColorMatrixFilter_DEFINED
 #define SkColorMatrixFilter_DEFINED
 
 #include "SkColorFilter.h"
 #include "SkColorMatrix.h"
 
 class SK_API SkColorMatrixFilter : public SkColorFilter {
 public:
     static SkColorMatrixFilter* Create(const SkColorMatrix& cm) {
         return SkNEW_ARGS(SkColorMatrixFilter, (cm));
     }
     static SkColorMatrixFilter* Create(const SkScalar array[20]) {
         return SkNEW_ARGS(SkColorMatrixFilter, (array));
     }
 
     // overrides from SkColorFilter
     void filterSpan(const SkPMColor src[], int count, SkPMColor[]) const SK_OVERRIDE;
     void filterSpan16(const uint16_t src[], int count, uint16_t[]) const SK_OVERRIDE;
     uint32_t getFlags() const SK_OVERRIDE;
     bool asColorMatrix(SkScalar matrix[20]) const SK_OVERRIDE;
+    SkColorFilter* newComposed(const SkColorFilter*) const SK_OVERRIDE;
+
 #if SK_SUPPORT_GPU
     GrFragmentProcessor* asFragmentProcessor(GrContext*) const SK_OVERRIDE;
 #endif
 
     struct State {
         int32_t fArray[20];
         int     fShift;
     };
 
     SK_TO_STRING_OVERRIDE()
@@ skipping 14 matching lines @@
     Proc        fProc;
     State       fState;
     uint32_t    fFlags;
 
     void initState(const SkScalar array[20]);
 
     typedef SkColorFilter INHERITED;
 };
 
 #endif