Move nullable_string16.h to the string subdirectory.

ipc/ipc_message_utils.h

 // Copyright (c) 2012 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 IPC_IPC_MESSAGE_UTILS_H_
 #define IPC_IPC_MESSAGE_UTILS_H_
 
 #include <algorithm>
 #include <map>
 #include <set>
@@ skipping 27 matching lines @@
 #else
 #define IPC_MSG_NOINLINE  __attribute__((noinline));
 #endif
 #elif defined(COMPILER_MSVC)
 // MSVC++ doesn't do this.
 #define IPC_MSG_NOINLINE
 #else
 #error "Please add the noinline property for your new compiler here."
 #endif
 
-class NullableString16;
-
 namespace base {
 class DictionaryValue;
 class FilePath;
 class ListValue;
+class NullableString16;
 class Time;
 class TimeDelta;
 class TimeTicks;
 struct FileDescriptor;
 }
 
 namespace IPC {
 
 struct ChannelHandle;
 
@@ skipping 383 matching lines @@
 
 template <>
 struct IPC_EXPORT ParamTraits<base::ListValue> {
   typedef base::ListValue param_type;
   static void Write(Message* m, const param_type& p);
   static bool Read(const Message* m, PickleIterator* iter, param_type* r);
   static void Log(const param_type& p, std::string* l);
 };
 
 template <>
-struct IPC_EXPORT ParamTraits<NullableString16> {
-  typedef NullableString16 param_type;
+struct IPC_EXPORT ParamTraits<base::NullableString16> {
+  typedef base::NullableString16 param_type;
   static void Write(Message* m, const param_type& p);
   static bool Read(const Message* m, PickleIterator* iter,
                    param_type* r);
   static void Log(const param_type& p, std::string* l);
 };
 
 template <>
 struct IPC_EXPORT ParamTraits<base::PlatformFileInfo> {
   typedef base::PlatformFileInfo param_type;
   static void Write(Message* m, const param_type& p);
@@ skipping 398 matching lines @@
   template<typename TA, typename TB, typename TC, typename TD, typename TE>
   static void WriteReplyParams(Message* reply, TA a, TB b, TC c, TD d, TE e) {
     ReplyParam p(a, b, c, d, e);
     WriteParam(reply, p);
   }
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_MESSAGE_UTILS_H_