Replace NinePieceImage.setMaskDefault with static method.

third_party/WebKit/Source/core/style/NinePieceImage.h

Index: third_party/WebKit/Source/core/style/NinePieceImage.h
diff --git a/third_party/WebKit/Source/core/style/NinePieceImage.h b/third_party/WebKit/Source/core/style/NinePieceImage.h
index 0e876f39b7303f8cb99da2f79750efb3ffa8ea8d..f7b87effdb54addcc3f458dbf3997689d1ca4d96 100644
--- a/third_party/WebKit/Source/core/style/NinePieceImage.h
+++ b/third_party/WebKit/Source/core/style/NinePieceImage.h
@@ -82,6 +82,14 @@ class CORE_EXPORT NinePieceImage {
                  ENinePieceImageRule horizontal_rule,
                  ENinePieceImageRule vertical_rule);
 
+  static NinePieceImage MaskDefaults() {
+    NinePieceImage image;
+    image.data_.Access()->image_slices = LengthBox(0);
+    image.data_.Access()->fill = true;
+    image.data_.Access()->border_slices = BorderImageLengthBox(Length(kAuto));
+    return image;
+  }
+
   bool operator==(const NinePieceImage& other) const {
     return data_ == other.data_;
   }
@@ -145,12 +153,6 @@ class CORE_EXPORT NinePieceImage {
     data_.Access()->vertical_rule = other.data_->vertical_rule;
   }
 
-  void SetMaskDefaults() {
-    data_.Access()->image_slices = LengthBox(0);
-    data_.Access()->fill = true;
-    data_.Access()->border_slices = BorderImageLengthBox(Length(kAuto));
-  }
-
   static LayoutUnit ComputeOutset(const BorderImageLength& outset_side,
                                   int border_side) {
     if (outset_side.IsNumber())