Make RootScroller set the outer viewport scroll layer in the compositor

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 {
 
 namespace {
 
 ScrollableArea* scrollableAreaFor(const Element& element)
 {
     if (!element.layoutObject() || !element.layoutObject()->isBox())
         return nullptr;
@@ skipping 126 matching lines @@
     // 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
     // in RootFrameViewport.
     m_viewportApplyScroll->setScroller(targetScroller);
 
     return true;
 }
 
+void RootScrollerController::didUpdateCompositing()
+{
+    FrameHost& frameHost = *m_document->frameHost();
+
+    // Let the compositor-side counterpart know about this change.
+    if (m_document->isInMainFrame())
+        frameHost.chromeClient().registerViewportLayers();
+}
+
+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;
+}
+
 Element* RootScrollerController::defaultEffectiveRootScroller()
 {
     DCHECK(m_document);
     return m_document->documentElement();
 }
 
 } // namespace blink