Add explicit keyword to constructors that take one argument

Source/core/css/CSSCanvasValue.h

 /*
  * Copyright (C) 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 32 matching lines @@
     PassRefPtr<Image> image(RenderObject*, const IntSize&);
     bool isFixedSize() const { return true; }
     IntSize fixedSize(const RenderObject*);
 
     bool isPending() const { return false; }
     void loadSubimages(ResourceFetcher*) { }
 
     bool equals(const CSSCanvasValue&) const;
 
 private:
-    CSSCanvasValue(const String& name)
+    explicit CSSCanvasValue(const String& name)
         : CSSImageGeneratorValue(CanvasClass)
         , m_canvasObserver(this)
         , m_name(name)
         , m_element(0)
     {
     }
 
     // NOTE: We put the CanvasObserver in a member instead of inheriting from it
     // to avoid adding a vptr to CSSCanvasValue.
     class CanvasObserverProxy : public CanvasObserver {
@@ skipping 26 matching lines @@
 
     // The name of the canvas.
     String m_name;
     // The document supplies the element and owns it.
     HTMLCanvasElement* m_element;
 };
 
 } // namespace WebCore
 
 #endif // CSSCanvasValue_h