Split RootScrollerController into top-document and child-document classes

third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h

Index: third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h
diff --git a/third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h b/third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h
index 9a0dae610cb946ede9c9ed38ceac0c980c2a869e..c28c4f5fed14b07a2d9fe9306f8dc26262be85d8 100644
--- a/third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h
+++ b/third_party/WebKit/Source/core/page/scrolling/RootScrollerController.h
@@ -13,41 +13,36 @@ namespace blink {
 class Document;
 class Element;
 class GraphicsLayer;
+class ScrollableArea;
 class ScrollStateCallback;
-class ViewportScrollCallback;
 
-// Manages the root scroller associated with a given document. The root scroller
-// causes top controls movement, overscroll effects and prevents chaining
-// scrolls up further in the DOM. It can be set from script using
+// Manages the root scroller associated with a given document. The root
+// scroller causes top controls movement, overscroll effects and prevents
+// chaining scrolls up further in the DOM. It can be set from script using
 // document.setRootScroller.
 //
 // There are two notions of a root scroller in this class: m_rootScroller and
 // m_effectiveRootScroller. The former is the Element that was set as the root
 // scroller using document.setRootScroller. If the page didn't set a root
 // scroller this will be nullptr. The "effective" root scroller is the current
-// element we're using internally to apply viewport scroll actions. i.e It's the
-// element with the ViewportScrollCallback set as its apply-scroll callback.
-// The effective root scroller will only be null during document initialization.
+// element we're using internally to apply viewport scrolling actions.  The
+// effective root scroller will only be null during document initialization.
 //
-// If the root scroller element is a valid element to become the root scroller,
-// it will be promoted to the effective root scroller. If it is not valid, the
-// effective root scroller will fall back to a default Element (see
+// If the currently set m_rootScroller is a valid element to become the root
+// scroller, it will be promoted to the effective root scroller. If it is not
+// valid, the effective root scroller will fall back to a default Element (see
 // defaultEffectiveRootScroller()). The rules for what makes an element a valid
 // root scroller are set in isValidRootScroller(). The validity of the current
 // root scroller is re-checked after each layout.
 class CORE_EXPORT RootScrollerController
     : public GarbageCollected<RootScrollerController> {
 public:
-    // Creates a RootScrollerController for the given document. You should use
-    // setViewportScrollCallback to provide this class with a scroll callback
-    // that RootScrollerController will keep applied to the current RootScroller
-    // so that special actions can occur on scrolling.
-    static RootScrollerController* create(Document& document)
-    {
-        return new RootScrollerController(document);
-    }
+    // Creates a RootScrollerController for the given document. Note, instances
+    // of this class need to be made aware of lifecycle events, see the
+    // didUpdateLayout, didUpdateCompositing, etc. type methods below.
+    static RootScrollerController* create(Document&);
 
-    DECLARE_TRACE();
+    DECLARE_VIRTUAL_TRACE();
 
     // Sets the element that will be used as the root scroller. This can be
     // nullptr, in which case we'll use the default element (documentElement) as
@@ -74,36 +69,50 @@ public:
 
     // This class needs to be informed of changes to compositing so that it can
     // update the compositor when the effective root scroller changes.
-    void didUpdateCompositing();
+    virtual void didUpdateCompositing();
 
     // This class needs to be informed when the document has been attached to a
     // FrameView so that we can initialize the viewport scroll callback.
-    void didAttachDocument();
+    virtual void didAttachDocument();
 
+    // Returns the GraphicsLayer for the current effective root scroller
+    // element.
     GraphicsLayer* rootScrollerLayer();
 
+    // Returns true if the given ScrollStateCallback is the ViewportScrollCallback managed
+    // by this class.
     // TODO(bokan): Temporarily needed to allow ScrollCustomization to
     // differentiate between real custom callback and the built-in viewport
-    // apply scroll.
-    bool isViewportScrollCallback(const ScrollStateCallback*) const;
+    // apply scroll. crbug.com/623079.
+    virtual bool isViewportScrollCallback(const ScrollStateCallback*) const;
 
-private:
+protected:
     RootScrollerController(Document&);
 
-    Element* defaultEffectiveRootScroller();
-
     // Ensures the effective root scroller is currently valid and replaces it
     // with the default if not.
-    void updateEffectiveRootScroller();
+    virtual void updateEffectiveRootScroller();
 
-    // Called only from the top Document's RootScrollerController. Ensures that
-    // the element that should be used as the root scroller on the page has the
-    // m_viewportApplyScroll callback set on it.
-    void setViewportApplyScrollOnRootScroller();
+    // Returns the ScrollableArea to use to scroll the given Element.
+    ScrollableArea* scrollableAreaFor(const Element&) const;
 
+    // The owning Document whose root scroller this object manages.
     WeakMember<Document> m_document;
-    Member<ViewportScrollCallback> m_viewportApplyScroll;
 
+private:
+
+    // Determines whether the given element meets the criteria to become the
+    // effective root scroller.
+    bool isValidRootScroller(const Element&) const;
+
+    // Returns the Element that should be used if the currently set
+    // m_rootScroller isn't valid to be a root scroller.
+    Element* defaultEffectiveRootScroller();
+
+    // The Element that was set from script as rootScroller. Depending on its
+    // validity to be the root scroller (e.g. a display: none element isn't a
+    // valid root scroller), this may not actually be the Element being used as
+    // the root scroller.
     WeakMember<Element> m_rootScroller;
 
     // The element currently being used as the root scroller. If
@@ -112,10 +121,6 @@ private:
     // initialization and will not be set until m_viewportApplyScroll is
     // provided.
     WeakMember<Element> m_effectiveRootScroller;
-
-    // Tracks which element currently has the m_viewportApplyScroll set to it.
-    // This will only ever be set on the top Document's RootScrollerController.
-    WeakMember<Element> m_currentViewportApplyScrollHost;
 };
 
 } // namespace blink