Fixed up root scroller API to be more webby

third_party/WebKit/Source/core/dom/Document.h

Index: third_party/WebKit/Source/core/dom/Document.h
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index 9d02504f37de9338f5d27c8c6af0be186c6468a4..5e7a4c1fd25681f007b8cc658e6a25d9accb9ab9 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -126,6 +126,7 @@ class IdleRequestOptions;
 class InputDeviceCapabilities;
 class IntersectionObserverController;
 class LayoutPoint;
+class LayoutView;
 class LayoutViewItem;
 class LiveNodeListBase;
 class Locale;
@@ -144,8 +145,8 @@ class PlatformMouseEvent;
 class ProcessingInstruction;
 class QualifiedName;
 class Range;
-class LayoutView;
 class ResourceFetcher;
+class RootScroller;
 class SVGDocumentExtensions;
 class SVGUseElement;
 class ScriptRunner;
@@ -1064,8 +1065,9 @@ public:
     ShadowCascadeOrder shadowCascadeOrder() const { return m_shadowCascadeOrder; }
     void setShadowCascadeOrder(ShadowCascadeOrder);
 
+    Element* rootScroller() const;
     void setRootScroller(Element*, ExceptionState&);
-    Element* rootScroller();
+    bool isEffectiveRootScroller(const Element*) const;
 
     bool isInMainFrame() const;
 
@@ -1220,6 +1222,7 @@ private:
     Member<Element> m_activeHoverElement;
     Member<Element> m_documentElement;
     UserActionElementSet m_userActionElements;
+    Member<RootScroller> m_rootScroller;
 
     uint64_t m_domTreeVersion;
     static uint64_t s_globalTreeVersion;