Add *explicit* keyword to avoid implicit type conversion

Source/core/svg/SVGDocumentExtensions.h

 /*
  * Copyright (C) 2006 Apple Inc. All rights reserved.
  * Copyright (C) 2006, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 26 matching lines @@
 #endif
 class SVGResourcesCache;
 class SVGSMILElement;
 class SVGSVGElement;
 class Element;
 
 class SVGDocumentExtensions {
     WTF_MAKE_NONCOPYABLE(SVGDocumentExtensions); WTF_MAKE_FAST_ALLOCATED;
 public:
     typedef HashSet<Element*> SVGPendingElements;
-    SVGDocumentExtensions(Document*);
+    explicit SVGDocumentExtensions(Document*);
     ~SVGDocumentExtensions();
 
     void addTimeContainer(SVGSVGElement*);
     void removeTimeContainer(SVGSVGElement*);
 
     void addResource(const AtomicString& id, RenderSVGResourceContainer*);
     void removeResource(const AtomicString& id);
     RenderSVGResourceContainer* resourceById(const AtomicString& id) const;
 
     static void serviceOnAnimationFrame(Document&, double monotonicAnimationStartTime);
@@ skipping 59 matching lines @@
     void markPendingResourcesForRemoval(const AtomicString&);
     Element* removeElementFromPendingResourcesForRemoval(const AtomicString&);
 
 private:
     PassOwnPtr<SVGPendingElements> removePendingResourceForRemoval(const AtomicString&);
 };
 
 }
 
 #endif