cc: Update SpreadForStdDeviation to 3*sigma, and update tests.

cc/output/filter_operation.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 
 #include <algorithm>
 
 #include "base/trace_event/trace_event_argument.h"
 #include "base/values.h"
@@ skipping 298 matching lines @@
           value->AppendInteger(it.rect().width());
           value->AppendInteger(it.rect().height());
         }
         value->EndArray();
       }
       break;
   }
 }
 
 static SkVector MapStdDeviation(float std_deviation, const SkMatrix& matrix) {
+  // Corresponds to SpreadForStdDeviation in filter_operations.cc.
   SkVector sigma = SkVector::Make(std_deviation, std_deviation);
   matrix.mapVectors(&sigma, 1);
   return sigma * SkIntToScalar(3);
 }
 
 gfx::Rect FilterOperation::MapRect(const gfx::Rect& rect,
                                    const SkMatrix& matrix) const {
   switch (type_) {
     case FilterOperation::BLUR: {
       SkVector spread = MapStdDeviation(amount(), matrix);
@@ skipping 16 matching lines @@
       SkIRect out_rect = image_filter()->filterBounds(
           in_rect, matrix, SkImageFilter::kForward_MapDirection);
       return gfx::SkIRectToRect(out_rect);
     }
     default:
       return rect;
   }
 }
 
 }  // namespace cc