Split RootScrollerController into top-document and child-document classes

third_party/WebKit/Source/core/page/scrolling/TopDocumentRootScrollerController.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 TopDocumentRootScrollerController_h
+#define TopDocumentRootScrollerController_h
+
+#include "core/CoreExport.h"
+#include "core/page/scrolling/RootScrollerController.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class Document;
+class Element;
+class GraphicsLayer;
+class ScrollStateCallback;
+class ViewportScrollCallback;
+
+// The RootScrollerController used to manage the root scroller for the top
+// level Document on a page. In addition to the regular RootScroller duties
+// such as keeping track of which Element is set as root scroller and which is
+// the effective root scroller, this class is also responsible for setting the
+// ViewportApplyScroll on the one Element on a page that should apply viewport
+// scrolling actions.
+class CORE_EXPORT TopDocumentRootScrollerController
+    : public RootScrollerController {
+public:
+    static TopDocumentRootScrollerController* create(Document&);
+
+    DECLARE_VIRTUAL_TRACE();
+
+    // This class needs to be informed of changes to compositing so that it can
+    // update the compositor when the effective root scroller changes.
+    void didUpdateCompositing() override;
+
+    // This class needs to be informed when the document has been attached to a
+    // FrameView so that we can initialize the viewport scroll callback.
+    void didAttachDocument() override;
+
+    // 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.
+    bool isViewportScrollCallback(
+        const ScrollStateCallback*) const override;
+
+protected:
+    TopDocumentRootScrollerController(Document&);
+
+    // Ensures the effective root scroller is currently valid and replaces it
+    // with the default if not.
+    void updateEffectiveRootScroller() override;
+
+private:
+    // Ensures that the element that should be used as the root scroller on the
+    // page has the m_viewportApplyScroll callback set on it.
+    void setViewportApplyScrollOnRootScroller();
+
+    // The apply-scroll callback that moves top controls and produces
+    // overscroll effects. This class makes sure this callback is set on the
+    // appropriate root scroller element.
+    Member<ViewportScrollCallback> m_viewportApplyScroll;
+
+    // Tracks which element currently has the m_viewportApplyScroll set to it.
+    WeakMember<Element> m_currentViewportApplyScrollHost;
+};
+
+} // namespace blink
+
+#endif // RootScrollerController_h