Make Maps constructor explicit.

maps.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MAPS_H__
 #define MAPS_H__
 
 #include <elf.h>
 #include <functional>
 #include <map>
@@ skipping 11 matching lines @@
 
 namespace playground {
 
 class Library;
 class Maps {
   friend class Library;
  public:
   typedef std::basic_string<char, std::char_traits<char>,
                             SystemAllocator<char> > string;
 
-  Maps(int proc_self_maps);
+  explicit Maps(int proc_self_maps);
   ~Maps();
 
  protected:
   // A map with all the libraries currently loaded into the application.
   // The key is a unique combination of device number, inode number, and
   // file name. It should be treated as opaque.
   typedef std::map<string, Library, std::less<string>,
                    SystemAllocator<std::pair<const string,
                                              Library> > > LibraryMap;
   friend class Iterator;
@@ skipping 43 matching lines @@
   const Iterator begin_iter_;
   const Iterator end_iter_;
 
   LibraryMap     libs_;
   char*          vsyscall_;
 };
 
 } // namespace
 
 #endif // MAPS_H__