Declare string16 traits’ move() correctly

base/strings/string16.h

 // Copyright 2013 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 BASE_STRINGS_STRING16_H_
 #define BASE_STRINGS_STRING16_H_
 
 // WHAT:
 // A version of std::basic_string that provides 2-byte characters even when
 // wchar_t is not implemented as a 2-byte type. You can access this class as
@@ skipping 76 matching lines @@
 
   static size_t length(const char_type* s) {
     return c16len(s);
   }
 
   static const char_type* find(const char_type* s, size_t n,
                                const char_type& a) {
     return c16memchr(s, a, n);
   }
 
-  static char_type* move(char_type* s1, const char_type* s2, int_type n) {
+  static char_type* move(char_type* s1, const char_type* s2, size_t n) {
     return c16memmove(s1, s2, n);
   }
 
   static char_type* copy(char_type* s1, const char_type* s2, size_t n) {
     return c16memcpy(s1, s2, n);
   }
 
   static char_type* assign(char_type* s, size_t n, char_type a) {
     return c16memset(s, a, n);
   }
@@ skipping 67 matching lines @@
 // boundaries, such as in statically-linked executables.
 //
 // TODO(mark): File this bug with Apple and update this note with a bug number.
 
 extern template
 class BASE_EXPORT std::basic_string<base::char16, base::string16_char_traits>;
 
 #endif  // WCHAR_T_IS_UTF32
 
 #endif  // BASE_STRINGS_STRING16_H_