Image filters: optimize crop rect application

include/effects/SkLightingImageFilter.h

 /*
  * Copyright 2012 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 SkLightingImageFilter_DEFINED
 #define SkLightingImageFilter_DEFINED
 
@@ skipping 31 matching lines @@
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
 
 protected:
     SkLightingImageFilter(SkImageFilterLight* light,
                           SkScalar surfaceScale,
                           SkImageFilter* input,
                           const CropRect* cropRect);
     void flatten(SkWriteBuffer&) const override;
     const SkImageFilterLight* light() const { return fLight.get(); }
     SkScalar surfaceScale() const { return fSurfaceScale; }
-    bool canComputeFastBounds() const override { return false; }
+    bool affectsTransparentBlack() const override { return true; }
 
 private:
     typedef SkImageFilter INHERITED;
     SkAutoTUnref<SkImageFilterLight> fLight;
     SkScalar fSurfaceScale;
 };
 
 #endif