Hide scrollbars when their dimensions are not scrollable.

Source/web/WebViewImpl.cpp

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 4283 matching lines @@
         m_doubleTapZoomPending = false;
     }
 }
 
 void WebViewImpl::updateLayerTreeViewport()
 {
     if (!page() || !m_layerTreeView)
         return;
 
     m_layerTreeView->setPageScaleFactorAndLimits(pageScaleFactor(), minimumPageScaleFactor(), maximumPageScaleFactor());
+
+    if (pinchVirtualViewportEnabled())
+        page()->frameHost().pinchViewport().adjustScrollbarExistence();
 }
 
 void WebViewImpl::updateLayerTreeBackgroundColor()
 {
     if (!m_layerTreeView)
         return;
 
     m_layerTreeView->setBackgroundColor(alphaChannel(m_backgroundColorOverride) ? m_backgroundColorOverride : backgroundColor());
 }
 
@@ skipping 129 matching lines @@
     const PageScaleConstraints& constraints = m_pageScaleConstraintsSet.pageDefinedConstraints();
 
     if (!mainFrameImpl() || !mainFrameImpl()->frameView())
         return false;
 
     return mainFrameImpl()->frameView()->layoutSize().width() == m_size.width
         || (constraints.minimumScale == constraints.maximumScale && constraints.minimumScale != -1);
 }
 
 } // namespace blink