Move TopDocumentRootScrollerController to a separate object on FrameHost

third_party/WebKit/Source/core/page/scrolling/RootScrollerUtil.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/RootScrollerUtil.h"
+
+#include "core/dom/Document.h"
+#include "core/dom/Element.h"
+#include "core/frame/FrameView.h"
+#include "core/layout/LayoutBox.h"
+#include "core/layout/LayoutObject.h"
+#include "core/paint/PaintLayerScrollableArea.h"
+
+namespace blink {
+
+namespace RootScrollerUtil {
+
+ScrollableArea* scrollableAreaFor(const Element& element)
+{
+    if (!element.layoutObject() || !element.layoutObject()->isBox())
+        return nullptr;
+
+    LayoutBox* box = toLayoutBox(element.layoutObject());
+
+    // For a FrameView, we use the layoutViewport rather than the
+    // getScrollableArea() since that could be the RootFrameViewport. The
+    // rootScroller's ScrollableArea will be swapped in as the layout viewport
+    // in RootFrameViewport so we need to ensure we get the layout viewport.
+    if (box->isDocumentElement())
+        return element.document().view()->layoutViewportScrollableArea();
+
+    return static_cast<PaintInvalidationCapableScrollableArea*>(
+        box->getScrollableArea());
+}
+
+} // namespace RootScrollerUtil
+
+} // namespace blink