Make document.rootScroller work properly across iframes.

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

 // 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.
 
 #include "core/page/scrolling/RootScrollerController.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
@@ skipping 47 matching lines @@
 DEFINE_TRACE(RootScrollerController)
 {
     visitor->trace(m_document);
     visitor->trace(m_rootScroller);
     visitor->trace(m_effectiveRootScroller);
 }
 
 void RootScrollerController::set(Element* newRootScroller)
 {
     m_rootScroller = newRootScroller;
-    updateEffectiveRootScroller();
+    recomputeEffectiveRootScroller();
 }
 
 Element* RootScrollerController::get() const
 {
     return m_rootScroller;
 }
 
 Element* RootScrollerController::effectiveRootScroller() const
 {
     return m_effectiveRootScroller;
 }
 
 void RootScrollerController::didUpdateLayout()
 {
-    updateEffectiveRootScroller();
+    recomputeEffectiveRootScroller();
 }
 
-void RootScrollerController::updateEffectiveRootScroller()
+void RootScrollerController::globalRootScrollerMayHaveChanged()
+{
+}
+
+void RootScrollerController::recomputeEffectiveRootScroller()
 {
     bool rootScrollerValid =
         m_rootScroller && isValidRootScroller(*m_rootScroller);
 
     Element* newEffectiveRootScroller = rootScrollerValid
         ? m_rootScroller.get()
         : defaultEffectiveRootScroller();
 
     if (m_effectiveRootScroller == newEffectiveRootScroller)
         return;
 
     m_effectiveRootScroller = newEffectiveRootScroller;
+
+    m_document->topDocument().rootScrollerController()
+        ->globalRootScrollerMayHaveChanged();
 }
 
 ScrollableArea* RootScrollerController::scrollableAreaFor(
     const Element& element) const
 {
     if (!element.layoutObject() || !element.layoutObject()->isBox())
         return nullptr;
 
     LayoutBox* box = toLayoutBox(element.layoutObject());
 
@@ skipping 25 matching lines @@
 void RootScrollerController::didUpdateCompositing()
 {
 }
 
 void RootScrollerController::didAttachDocument()
 {
 }
 
 GraphicsLayer* RootScrollerController::rootScrollerLayer()
 {
-    if (!m_effectiveRootScroller)
-        return nullptr;
-
-    ScrollableArea* area = scrollableAreaFor(*m_effectiveRootScroller);
-
-    if (!area)
-        return nullptr;
-
-    GraphicsLayer* graphicsLayer = area->layerForScrolling();
-
-    // TODO(bokan): We should assert graphicsLayer here and
-    // RootScrollerController should do whatever needs to happen to ensure
-    // the root scroller gets composited.
-
-    return graphicsLayer;
+    NOTREACHED();
+    return nullptr;
 }
 
 bool RootScrollerController::isViewportScrollCallback(
     const ScrollStateCallback* callback) const
 {
     // TopDocumentRootScrollerController must override this method to actually
     // do the comparison.
     DCHECK(!m_document->isInMainFrame());
 
     RootScrollerController* topDocumentController =
         m_document->topDocument().rootScrollerController();
     return topDocumentController->isViewportScrollCallback(callback);
 }
 
 Element* RootScrollerController::defaultEffectiveRootScroller()
 {
     DCHECK(m_document);
     return m_document->documentElement();
 }
 
 } // namespace blink