Disable overlay scrollbars in Blink when hidden by the compositor.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 3680 matching lines @@
         (shouldPlaceVerticalScrollbarOnLeft() && m_verticalScrollbar)
             ? m_verticalScrollbar->width()
             : 0,
         height() - thickness,
         width() - (m_verticalScrollbar ? m_verticalScrollbar->width() : 0),
         thickness);
     m_horizontalScrollbar->setFrameRect(hBarRect);
     if (oldRect != m_horizontalScrollbar->frameRect())
       setScrollbarNeedsPaintInvalidation(HorizontalScrollbar);
 
-    m_horizontalScrollbar->setEnabled(contentsWidth() > clientWidth);
+    m_horizontalScrollbar->setEnabled(contentsWidth() > clientWidth &&
+                                      !scrollbarsHidden());
     m_horizontalScrollbar->setProportion(clientWidth, contentsWidth());
     m_horizontalScrollbar->offsetDidChange();
   }
 
   if (m_verticalScrollbar) {
     int thickness = m_verticalScrollbar->scrollbarThickness();
     int clientHeight = visibleHeight();
     IntRect oldRect(m_verticalScrollbar->frameRect());
     IntRect vBarRect(
         shouldPlaceVerticalScrollbarOnLeft() ? 0 : (width() - thickness), 0,
         thickness,
         height() -
             (m_horizontalScrollbar ? m_horizontalScrollbar->height() : 0));
     m_verticalScrollbar->setFrameRect(vBarRect);
     if (oldRect != m_verticalScrollbar->frameRect())
       setScrollbarNeedsPaintInvalidation(VerticalScrollbar);
 
-    m_verticalScrollbar->setEnabled(contentsHeight() > clientHeight);
+    m_verticalScrollbar->setEnabled(contentsHeight() > clientHeight &&
+                                    !scrollbarsHidden());
     m_verticalScrollbar->setProportion(clientHeight, contentsHeight());
     m_verticalScrollbar->offsetDidChange();
   }
 }
 
 bool FrameView::adjustScrollbarExistence(
     ComputeScrollbarExistenceOption option) {
   ASSERT(m_inUpdateScrollbars);
 
   // If we came in here with the view already needing a layout, then go ahead
@@ skipping 47 matching lines @@
   return m_frame->settings()->ignoreMainFrameOverflowHiddenQuirk() &&
          m_frame->isMainFrame();
 }
 
 void FrameView::updateScrollbarsIfNeeded() {
   if (m_needsScrollbarsUpdate || needsScrollbarReconstruction() ||
       scrollOriginChanged())
     updateScrollbars();
 }
 
+void FrameView::didChangeScrollbarsHidden() {
+  updateScrollbars();
+}
+
 void FrameView::updateScrollbars() {
   m_needsScrollbarsUpdate = false;
 
   if (RuntimeEnabledFeatures::rootLayerScrollingEnabled())
     return;
 
   // Avoid drawing two sets of scrollbars when visual viewport is enabled.
   if (visualViewportSuppliesScrollbars()) {
     setHasHorizontalScrollbar(false);
     setHasVerticalScrollbar(false);
@@ skipping 710 matching lines @@
   DCHECK(m_frame->isMainFrame());
   return m_initialViewportSize.width();
 }
 
 int FrameView::initialViewportHeight() const {
   DCHECK(m_frame->isMainFrame());
   return m_initialViewportSize.height();
 }
 
 }  // namespace blink