Fixed up root scroller API to be more webby

third_party/WebKit/Source/core/input/EventHandler.cpp

Index: third_party/WebKit/Source/core/input/EventHandler.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index 0aa7ebcf9babbe3fcd8f9422e7bee6cf1f2b8303..435c8e7908f2aa5737c5d5c0a00431e0e8aeef07 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -602,10 +602,6 @@ ScrollResult EventHandler::scrollBox(LayoutBox* box,
         return box->scroll(granularity, delta);
     }
 
-    // Viewport actions should only happen when scrolling an element in the
-    // main frame.
-    ASSERT(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.
@@ -2428,12 +2424,13 @@ WebInputEventResult EventHandler::handleGestureScrollBegin(const PlatformGesture
 
 bool EventHandler::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;
+
+    if (!node.isElementNode())
         return false;
 
-    return frameHost()->rootScroller()->get() == &node;
+    return m_frame->document()->topDocument().isEffectiveRootScroller(toElement(&node));

[esprehn, 2016/05/11 17:37:05]

your method should take a const Element&, then do toElement(node) here

[bokan, 2016/06/02 15:49:55]

Done.

 }
 
 WebInputEventResult EventHandler::handleGestureScrollUpdate(const PlatformGestureEvent& gestureEvent)