Move IDMap back to base/ where it is needed.

base/id_map.h

Index: base/id_map.h
diff --git a/chrome/common/id_map.h b/base/id_map.h
similarity index 97%
rename from chrome/common/id_map.h
rename to base/id_map.h
index bf351b8ae3573afbbc1a98b963cd86d492050f37..13fb2f29b920c22b86f261b1c587a1591ea23bfd 100644
--- a/chrome/common/id_map.h
+++ b/base/id_map.h
@@ -2,8 +2,8 @@
 // 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>
 
@@ -159,4 +159,4 @@ class IDMap {
   DISALLOW_COPY_AND_ASSIGN(IDMap);
 };
 
-#endif  // CHROME_COMMON_ID_MAP_H_
+#endif  // BASE_ID_MAP_H_