Remove document.rootScroller compositing clipping effects.

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 114 matching lines @@
     return;
 
   if (m_globalRootScroller)
     m_globalRootScroller->removeApplyScroll();
 
   // Use disable-native-scroll since the ViewportScrollCallback needs to
   // apply scroll actions both before (BrowserControls) and after (overscroll)
   // scrolling the element so it will apply scroll to the element itself.
   target->setApplyScroll(m_viewportApplyScroll, "disable-native-scroll");
 
-  // 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 =
       RootScrollerUtil::scrollableAreaForRootScroller(m_globalRootScroller);
 
   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_page || !m_page->mainFrame() || !m_page->mainFrame()->isLocalFrame())
     return nullptr;
 
   return toLocalFrame(m_page->mainFrame())->document();
 }
 
-void TopDocumentRootScrollerController::
-    setNeedsCompositingInputsUpdateOnGlobalRootScroller() {
-  if (!m_globalRootScroller)
-    return;
-
-  PaintLayer* layer = m_globalRootScroller->document()
-                          .rootScrollerController()
-                          .rootScrollerPaintLayer();
-
-  if (layer)
-    layer->setNeedsCompositingInputsUpdate();
-
-  if (LayoutView* view = m_globalRootScroller->document().layoutView()) {
-    view->compositor()->setNeedsCompositingUpdate(CompositingUpdateRebuildTree);
-  }
-}
-
 void TopDocumentRootScrollerController::didUpdateCompositing() {
   if (!m_page)
     return;
 
   // Let the compositor-side counterpart know about this change.
   m_page->chromeClient().registerViewportLayers();
 }
 
 void TopDocumentRootScrollerController::didDisposeScrollableArea(
     ScrollableArea& area) {
@@ skipping 51 matching lines @@
 
 PaintLayer* TopDocumentRootScrollerController::rootScrollerPaintLayer() const {
   return RootScrollerUtil::paintLayerForRootScroller(m_globalRootScroller);
 }
 
 Element* TopDocumentRootScrollerController::globalRootScroller() const {
   return m_globalRootScroller.get();
 }
 
 }  // namespace blink