Scale the ALPHA_THRESHOLD filter's region based on the device scale factor.

cc/output/render_surface_filters.cc

 // Copyright 2012 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 "cc/output/render_surface_filters.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "cc/output/filter_operation.h"
@@ skipping 144 matching lines @@
   skia::RefPtr<SkColorFilter> color_filter =
       skia::AdoptRef(SkColorMatrixFilter::Create(matrix));
   return skia::AdoptRef(
       SkColorFilterImageFilter::Create(color_filter.get(), input.get()));
 }
 
 }  // namespace
 
 skia::RefPtr<SkImageFilter> RenderSurfaceFilters::BuildImageFilter(
     const FilterOperations& filters,
+    const gfx::Vector2dF& scale,
     const gfx::SizeF& size) {
   skia::RefPtr<SkImageFilter> image_filter;
   SkScalar matrix[20];
   for (size_t i = 0; i < filters.size(); ++i) {
     const FilterOperation& op = filters.at(i);
     switch (op.type()) {
       case FilterOperation::GRAYSCALE:
         GetGrayscaleMatrix(1.f - op.amount(), matrix);
         image_filter = CreateMatrixImageFilter(matrix, image_filter);
         break;
@@ skipping 81 matching lines @@
           image_filter = CreateMatrixImageFilter(matrix, image_filter);
         } else if (image_filter) {
           image_filter = skia::AdoptRef(SkComposeImageFilter::Create(
               op.image_filter().get(), image_filter.get()));
         } else {
           image_filter = op.image_filter();
         }
         break;
       }
       case FilterOperation::ALPHA_THRESHOLD: {
-        skia::RefPtr<SkImageFilter> alpha_filter = skia::AdoptRef(
-            SkAlphaThresholdFilter::Create(
-                op.region(), op.amount(), op.outer_threshold()));
+        SkMatrix transform;
+        transform.setScale(scale.x(), scale.y());
+        skia::RefPtr<SkImageFilter> alpha_filter =
+            skia::AdoptRef(SkAlphaThresholdFilter::Create(
+                op.region(), transform, op.amount(), op.outer_threshold()));
         if (image_filter.get()) {
           image_filter = skia::AdoptRef(SkComposeImageFilter::Create(
               alpha_filter.get(), image_filter.get()));
         } else {
           image_filter = alpha_filter;
         }
         break;
       }
     }
   }
   return image_filter;
 }
 
 }  // namespace cc