Mark the AtomicString(const String&) constructor as explicit

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 1264 matching lines @@
     m_frame->document()->mediaQueryAffectingValueChanged();
     m_mediaType = mediaType;
 }
 
 AtomicString FrameView::mediaType() const
 {
     // See if we have an override type.
     String overrideType;
     InspectorInstrumentation::applyEmulatedMedia(m_frame.get(), &overrideType);
     if (!overrideType.isNull())
-        return overrideType;
+        return AtomicString(overrideType);
     return m_mediaType;
 }
 
 void FrameView::adjustMediaTypeForPrinting(bool printing)
 {
     if (printing) {
         if (m_mediaTypeWhenNotPrinting.isNull())
             m_mediaTypeWhenNotPrinting = mediaType();
             setMediaType("print");
     } else {
@@ skipping 2209 matching lines @@
 void FrameView::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 } // namespace WebCore