Add explicit keyword to constructors that take one argument

Source/core/css/CSSLineBoxContainValue.h

 /*
  * Copyright (C) 2011 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 35 matching lines @@
     }
 
     String customCssText() const;
     bool equals(const CSSLineBoxContainValue& other) const { return m_value == other.m_value; }
     LineBoxContain value() const { return m_value; }
 
 private:
     LineBoxContain m_value;
 
 private:
-    CSSLineBoxContainValue(LineBoxContain);
+    explicit CSSLineBoxContainValue(LineBoxContain);
 };
 
 } // namespace
 
 #endif