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

cc/output/render_surface_filters.cc

Index: cc/output/render_surface_filters.cc
diff --git a/cc/output/render_surface_filters.cc b/cc/output/render_surface_filters.cc
index 34e056dad521be2fa8a3260c904790aceee3fa3d..a01cba64618d476e0723467e888542125d1f7b15 100644
--- a/cc/output/render_surface_filters.cc
+++ b/cc/output/render_surface_filters.cc
@@ -162,6 +162,7 @@ skia::RefPtr<SkImageFilter> CreateMatrixImageFilter(
 
 skia::RefPtr<SkImageFilter> RenderSurfaceFilters::BuildImageFilter(
     const FilterOperations& filters,
+    const gfx::Vector2dF& scale,
     const gfx::SizeF& size) {
   skia::RefPtr<SkImageFilter> image_filter;
   SkScalar matrix[20];
@@ -263,9 +264,11 @@ skia::RefPtr<SkImageFilter> RenderSurfaceFilters::BuildImageFilter(
         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()));