Cleanup and refactor RootScrollerController.

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"
 #include "core/frame/TopControls.h"
 #include "core/frame/VisualViewport.h"
 #include "core/layout/LayoutBox.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/Page.h"
 #include "core/page/scrolling/OverscrollController.h"
 #include "core/page/scrolling/ViewportScrollCallback.h"
 #include "core/paint/PaintLayerScrollableArea.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/scroll/ScrollableArea.h"
 
 namespace blink {
 
+class RootFrameViewport;
+
 namespace {
 
 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
@@ skipping 50 matching lines @@
     : m_document(&document)
 {
 }
 
 DEFINE_TRACE(RootScrollerController)
 {
     visitor->trace(m_document);
     visitor->trace(m_viewportApplyScroll);
     visitor->trace(m_rootScroller);
     visitor->trace(m_effectiveRootScroller);
+    visitor->trace(m_currentViewportApplyScrollHost);
 }
 
 void RootScrollerController::set(Element* newRootScroller)
 {
     m_rootScroller = newRootScroller;
     updateEffectiveRootScroller();
 }
 
 Element* RootScrollerController::get() const
 {
     return m_rootScroller;
 }
 
 Element* RootScrollerController::effectiveRootScroller() const
 {
     return m_effectiveRootScroller;
 }
 
 void RootScrollerController::didUpdateLayout()
 {
     updateEffectiveRootScroller();
 }
 
-void RootScrollerController::setViewportScrollCallback(ViewportScrollCallback* callback)
-{
-    m_viewportApplyScroll = callback;
-    moveViewportApplyScroll(m_effectiveRootScroller);
-}
-
 void RootScrollerController::updateEffectiveRootScroller()
 {
     bool rootScrollerValid =
         m_rootScroller && isValidRootScroller(*m_rootScroller);
 
     Element* newEffectiveRootScroller = rootScrollerValid
         ? m_rootScroller.get()
         : defaultEffectiveRootScroller();
 
     if (m_effectiveRootScroller == newEffectiveRootScroller)
         return;
 
-    if (moveViewportApplyScroll(newEffectiveRootScroller))
-        m_effectiveRootScroller = newEffectiveRootScroller;
+    m_effectiveRootScroller = newEffectiveRootScroller;
+
+    if (m_document->isInMainFrame())
+        setViewportApplyScrollOnRootScroller();
 }
 
-bool RootScrollerController::moveViewportApplyScroll(Element* target)
+void RootScrollerController::setViewportApplyScrollOnRootScroller()
 {
-    if (!m_viewportApplyScroll || !target)
-        return false;
+    DCHECK(m_document->isInMainFrame());
 
-    ScrollableArea* targetScroller = scrollableAreaFor(*target);
+    if (!m_viewportApplyScroll || !m_effectiveRootScroller)
+        return;
+
+    ScrollableArea* targetScroller =
+        scrollableAreaFor(*m_effectiveRootScroller);
+
     if (!targetScroller)
-        return false;
+        return;
 
-    if (m_effectiveRootScroller)
-        m_effectiveRootScroller->removeApplyScroll();
+    if (m_currentViewportApplyScrollHost)
+        m_currentViewportApplyScrollHost->removeApplyScroll();
 
     // Use disable-native-scroll since the ViewportScrollCallback needs to
     // apply scroll actions both before (TopControls) and after (overscroll)
     // scrolling the element so it will apply scroll to the element itself.
-    target->setApplyScroll(m_viewportApplyScroll, "disable-native-scroll");
+    m_effectiveRootScroller->setApplyScroll(
+        m_viewportApplyScroll, "disable-native-scroll");
+
+    m_currentViewportApplyScrollHost = m_effectiveRootScroller;
 
     // Ideally, scroll customization would pass the current element to scroll to
     // the apply scroll callback but this doesn't happen today so we set it
     // through a back door here. This is also needed by the
-    // RootViewportScrollCallback to swap the target into the layout viewport
+    // ViewportScrollCallback to swap the target into the layout viewport
     // in RootFrameViewport.
     m_viewportApplyScroll->setScroller(targetScroller);
-
-    return true;
 }
 
 void RootScrollerController::didUpdateCompositing()
 {
-    FrameHost& frameHost = *m_document->frameHost();
+    FrameHost* frameHost = m_document->frameHost();
 
     // Let the compositor-side counterpart know about this change.
-    if (m_document->isInMainFrame())
-        frameHost.chromeClient().registerViewportLayers();
+    if (frameHost && m_document->isInMainFrame())
+        frameHost->chromeClient().registerViewportLayers();
+}
+
+void RootScrollerController::didAttachDocument()
+{
+    if (!m_document->isInMainFrame())
+        return;
+
+    FrameHost* frameHost = m_document->frameHost();
+    FrameView* frameView = m_document->view();
+
+    if (!frameHost || !frameView)
+        return;
+
+    RootFrameViewport* rootFrameViewport = frameView->getRootFrameViewport();
+    DCHECK(rootFrameViewport);
+
+    m_viewportApplyScroll = ViewportScrollCallback::create(
+        &frameHost->topControls(),
+        &frameHost->overscrollController(),
+        *rootFrameViewport);
+
+    updateEffectiveRootScroller();
 }
 
 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;
 }
 
+bool RootScrollerController::isViewportScrollCallback(
+    const ScrollStateCallback* callback) const
+{
+    if (!callback)
+        return false;
+
+    return callback == m_viewportApplyScroll.get();
+}
+
 Element* RootScrollerController::defaultEffectiveRootScroller()
 {
     DCHECK(m_document);
     return m_document->documentElement();
 }
 
 } // namespace blink