Image filters: optimize crop rect application

src/effects/SkPaintImageFilter.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPaintImageFilter.h"
 #include "SkCanvas.h"
 #include "SkReadBuffer.h"
@@ skipping 48 matching lines @@
         inverse.mapRect(&rect);
     }
     canvas->setMatrix(matrix);
     canvas->drawRect(rect, fPaint);
 
     offset->fX = bounds.fLeft;
     offset->fY = bounds.fTop;
     return surf->makeImageSnapshot();
 }
 
-bool SkPaintImageFilter::canComputeFastBounds() const {
-    // http:skbug.com/4627: "make computeFastBounds and onFilterBounds() CropRect-aware"
-    // computeFastBounds() doesn't currently take the crop rect into account,
-    // so we can't compute it. If a full crop rect is set, we should return true here.
-    return false;
+bool SkPaintImageFilter::affectsTransparentBlack() const {
+    return true;
 }
 
 #ifndef SK_IGNORE_TO_STRING
 void SkPaintImageFilter::toString(SkString* str) const {
     str->appendf("SkPaintImageFilter: (");
     fPaint.toString(str);
     str->append(")");
 }
 #endif