Move IDMap back to base/ where it is needed.

base/id_map.h

 // Copyright (c) 2006-2008 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 CHROME_COMMON_ID_MAP_H_
-#define CHROME_COMMON_ID_MAP_H_
+#ifndef BASE_ID_MAP_H_
+#define BASE_ID_MAP_H_
 
 #include <set>
 
 #include "base/basictypes.h"
 #include "base/hash_tables.h"
 #include "base/logging.h"
 
 // This object maintains a list of IDs that can be quickly converted to
 // pointers to objects. It is implemented as a hash table, optimized for
 // relatively small data sets (in the common case, there will be exactly one
@@ skipping 135 matching lines @@
   int32 next_id_;
 
   HashTable data_;
 
   // See description above setter.
   bool check_on_null_data_;
 
   DISALLOW_COPY_AND_ASSIGN(IDMap);
 };
 
-#endif  // CHROME_COMMON_ID_MAP_H_
+#endif  // BASE_ID_MAP_H_