Reland of Implement canComputeFastBounds() for image filters.

include/core/SkColorFilter.h

 /*
  * Copyright 2006 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 SkColorFilter_DEFINED
 #define SkColorFilter_DEFINED
 
@@ skipping 122 matching lines @@
      *  The fragment processor(s) must each return their color as a premul normalized value
      *  e.g. each component between [0..1] and each color component <= alpha.
      *
      *  If the subclass returns false, then it should not modify the array at all.
      */
     virtual bool asFragmentProcessors(GrContext*, GrProcessorDataManager*,
                                       SkTDArray<GrFragmentProcessor*>*) const {
         return false;
     }
 
+    bool affectsTransparentBlack() const {
+        return this->filterColor(0) != 0;
+    }
+
     SK_TO_STRING_PUREVIRT()
 
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
     SK_DEFINE_FLATTENABLE_TYPE(SkColorFilter)
 
 protected:
     SkColorFilter() {}
 
 private:
     /*
      *  Returns 1 if this is a single filter (not a composition of other filters), otherwise it
      *  reutrns the number of leaf-node filters in a composition. This should be the same value
      *  as the number of GrFragmentProcessors returned by asFragmentProcessors's array parameter.
      *
      *  e.g. compose(filter, compose(compose(filter, filter), filter)) --> 4
      */
     virtual int privateComposedFilterCount() const { return 1; }
     friend class SkComposeColorFilter;
 
     typedef SkFlattenable INHERITED;
 };
 
 #endif