Add a UA style, "display: contents", for <slot>

third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.h

Index: third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.h
diff --git a/third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.h b/third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.h
index c04806004d0705784766620982a822b68ab553f4..6a1f434ff99903766186bca2b4de0c0c25a615c4 100644
--- a/third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.h
+++ b/third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.h
@@ -61,6 +61,7 @@ class CSSDefaultStyleSheets : public GarbageCollected<CSSDefaultStyleSheets> {
   StyleSheetContents* fullscreenStyleSheet() {
     return m_fullscreenStyleSheet.get();
   }
+  StyleSheetContents* slotStyleSheet() { return m_slotStyleSheet.get(); }
 
   DECLARE_TRACE();
 
@@ -81,6 +82,7 @@ class CSSDefaultStyleSheets : public GarbageCollected<CSSDefaultStyleSheets> {
   Member<StyleSheetContents> m_mathmlStyleSheet;
   Member<StyleSheetContents> m_mediaControlsStyleSheet;
   Member<StyleSheetContents> m_fullscreenStyleSheet;
+  Member<StyleSheetContents> m_slotStyleSheet;
 };
 
 }  // namespace blink