Fixed up root scroller API to be more webby

third_party/WebKit/Source/core/input/ScrollManager.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/input/ScrollManager.h"
 
 #include "core/dom/DOMNodeIds.h"
 #include "core/events/GestureEvent.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
@@ skipping 224 matching lines @@
     DCHECK(box);
     Node* node = box->node();
 
     // If there's no ApplyScroll callback on the element, scroll as usuall in
     // the non-scroll-customization case.
     if (!node || !node->isElementNode() || !toElement(node)->getApplyScroll()) {
         *wasRootScroller = false;
         return box->scroll(granularity, delta);
     }
 
-    // Viewport actions should only happen when scrolling an element in the
-    // main frame.
-    DCHECK(m_frame->isMainFrame());
-
     // If there is an ApplyScroll callback, its because we placed one on the
     // root scroller to control top controls and overscroll. Invoke a scroll
     // using parts of the scroll customization framework on just this element.
     computeScrollChainForSingleNode(*node, m_currentScrollChain);
 
     OwnPtr<ScrollStateData> scrollStateData = adoptPtr(new ScrollStateData());
     scrollStateData->delta_x = delta.width();
     scrollStateData->delta_y = delta.height();
     scrollStateData->position_x = position.x();
     scrollStateData->position_y = position.y();
@@ skipping 226 matching lines @@
     if (!widget || !widget->isFrameView())
         return WebInputEventResult::NotHandled;
 
     return toFrameView(widget)->frame().eventHandler().handleGestureScrollEvent(gestureEvent);
 }
 
 bool ScrollManager::isRootScroller(const Node& node) const
 {
     // The root scroller is the one Element on the page designated to perform
     // "viewport actions" like top controls movement and overscroll glow.
-    if (!frameHost() || !frameHost()->rootScroller())
+    if (!m_frame->document())
         return false;
 
-    return frameHost()->rootScroller()->get() == &node;
+    if (!node.isElementNode())
+        return false;
+
+    return m_frame->document()->topDocument().isEffectiveRootScroller(toElement(node));
 }
 
 
 WebInputEventResult ScrollManager::handleGestureScrollEvent(const PlatformGestureEvent& gestureEvent)
 {
     Node* eventTarget = nullptr;
     Scrollbar* scrollbar = nullptr;
     if (gestureEvent.type() != PlatformEvent::GestureScrollBegin) {
         scrollbar = m_scrollbarHandlingScrollGesture.get();
         eventTarget = m_scrollGestureHandlingNode.get();
@@ skipping 139 matching lines @@
 DEFINE_TRACE(ScrollManager)
 {
     visitor->trace(m_frame);
     visitor->trace(m_scrollGestureHandlingNode);
     visitor->trace(m_previousGestureScrolledNode);
     visitor->trace(m_scrollbarHandlingScrollGesture);
     visitor->trace(m_resizeScrollableArea);
 }
 
 } // namespace blink