Make document.rootScroller work properly across iframes.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef RootScrollerController_h
 #define RootScrollerController_h
 
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class Document;
 class Element;
 class GraphicsLayer;
 class ScrollableArea;
 class ScrollStateCallback;
 
 // 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 scrolling actions.  The
 // effective root scroller will only be null during document initialization.
+// Both these elements are from this controller's associated Document. The final
+// "global" root scroller, the one whose scrolling hides top controls, may be in
+// a different frame.
 //
 // 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:
@@ skipping 30 matching lines @@
     // This class needs to be informed of changes to compositing so that it can
     // update the compositor when the effective root scroller changes.
     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.
     virtual void didAttachDocument();
 
     // Returns the GraphicsLayer for the current effective root scroller
     // element.
-    GraphicsLayer* rootScrollerLayer();
+    virtual GraphicsLayer* rootScrollerLayer();
 
-    // Returns true if the given ScrollStateCallback is the ViewportScrollCallback managed
-    // by this class.
+    // 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. crbug.com/623079.
     virtual bool isViewportScrollCallback(const ScrollStateCallback*) const;
 
 protected:
     RootScrollerController(Document&);
 
-    // Ensures the effective root scroller is currently valid and replaces it
-    // with the default if not.
-    virtual void updateEffectiveRootScroller();
+    // Called when the root scroller of any descendant frames changes. This
+    // will only ever be called on the top document's RootScrollerController.
+    virtual void globalRootScrollerMayHaveChanged();
 
     // 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;
 
 private:
 
+    // Ensures the effective root scroller is currently valid and replaces it
+    // with the default if not.
+    void recomputeEffectiveRootScroller();
+
     // 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.
+    // The Element that was set from script as rootScroller for this Document.
+    // 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
-    // m_viewportApplyScroll has been set, this element is guaranteed to have it
-    // set as its applyScroll callback. This can be nullptr during
-    // initialization and will not be set until m_viewportApplyScroll is
-    // provided.
+    // The element currently being used as the root scroller in this Document.
+    // If the m_rootScroller is valid this will point to it. Otherwise, it'll
+    // use a default Element.
     WeakMember<Element> m_effectiveRootScroller;
 };
 
 } // namespace blink
 
 #endif // RootScrollerController_h