Implement RefCountedCopyable<T>.

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

Index: third_party/WebKit/Source/core/style/StyleBoxData.h
diff --git a/third_party/WebKit/Source/core/style/StyleBoxData.h b/third_party/WebKit/Source/core/style/StyleBoxData.h
index 89c9cbdb99821350d54631b1fce4d5561e349e8d..4ce092d06749a70cbf91928b205dd16a0e8a1e78 100644
--- a/third_party/WebKit/Source/core/style/StyleBoxData.h
+++ b/third_party/WebKit/Source/core/style/StyleBoxData.h
@@ -36,7 +36,7 @@ namespace blink {
 // TODO(sashab): Move this into a private class on ComputedStyle, and remove
 // all methods on it, merging them into copy/creation methods on ComputedStyle
 // instead. Keep the allocation logic, only allocating a new object if needed.
-class CORE_EXPORT StyleBoxData : public RefCounted<StyleBoxData> {
+class CORE_EXPORT StyleBoxData : public RefCountedCopyable<StyleBoxData> {
  public:
   static PassRefPtr<StyleBoxData> create() {
     return adoptRef(new StyleBoxData);
@@ -71,7 +71,7 @@ class CORE_EXPORT StyleBoxData : public RefCounted<StyleBoxData> {
   friend class ComputedStyle;
 
   StyleBoxData();
-  StyleBoxData(const StyleBoxData&);
+  StyleBoxData(const StyleBoxData&) = default;
 
   Length m_width;
   Length m_height;