Disable scrollbars on the root scroller when using visual viewport scrollbars.

third_party/WebKit/Source/core/page/scrolling/TopDocumentRootScrollerController.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/TopDocumentRootScrollerController.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
@@ skipping 96 matching lines @@
 
   // A change in global root scroller requires a compositing inputs update to
   // the new and old global root scroller since it might change how the
   // ancestor layers are clipped. e.g. An iframe that's the global root
   // scroller clips its layers like the root frame.  Normally this is set
   // when the local effective root scroller changes but the global root
   // scroller can change because the parent's effective root scroller
   // changes.
   setNeedsCompositingInputsUpdateOnGlobalRootScroller();
 
+  ScrollableArea* oldRootScrollerArea =
+      m_globalRootScroller
+          ? RootScrollerUtil::scrollableAreaFor(*m_globalRootScroller.get())
+          : nullptr;
+
   m_globalRootScroller = target;
 
   setNeedsCompositingInputsUpdateOnGlobalRootScroller();
 
   // 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
   // ViewportScrollCallback to swap the target into the layout viewport
   // in RootFrameViewport.
   m_viewportApplyScroll->setScroller(targetScroller);
+
+  // The scrollers may need to stop using their own scrollbars as Android
+  // Chrome's VisualViewport provides the scrollbars for the root scroller.
+  if (oldRootScrollerArea)
+    oldRootScrollerArea->didChangeGlobalRootScroller();
+
+  targetScroller->didChangeGlobalRootScroller();
 }
 
 Document* TopDocumentRootScrollerController::topDocument() const {
   if (!m_frameHost)
     return nullptr;
 
   if (!m_frameHost->page().mainFrame() ||
       !m_frameHost->page().mainFrame()->isLocalFrame())
     return nullptr;
 
@@ skipping 64 matching lines @@
 
 PaintLayer* TopDocumentRootScrollerController::rootScrollerPaintLayer() const {
   return RootScrollerUtil::paintLayerFor(m_globalRootScroller);
 }
 
 Element* TopDocumentRootScrollerController::globalRootScroller() const {
   return m_globalRootScroller.get();
 }
 
 }  // namespace blink