Added basic client hints support.

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 4032 matching lines @@
     if (scrollOrigin() == origin)
         return;
 
     ScrollableArea::setScrollOrigin(origin);
 
     // Update if the scroll origin changes, since our position will be different if the content size did not change.
     if (updatePositionAtAll && updatePositionSynchronously)
         updateScrollbars(scrollOffsetDouble());
 }
 
+int FrameView::viewportWidth() const
+{
+    int viewportWidth = layoutSize(IncludeScrollbars).width();
+    return adjustForAbsoluteZoom(viewportWidth, renderView());
+}
+
 ScrollableArea* FrameView::scrollableArea()
 {
     Settings* settings = frame().settings();
     if (!settings || !settings->rootLayerScrolls())
         return this;
 
     RenderView* renderView = this->renderView();
     return renderView ? renderView->scrollableArea() : nullptr;
 }
 
 } // namespace blink