Make possible using pointer as a hash_table key when compiling using GCC.

base/hash_tables.h

Index: base/hash_tables.h
diff --git a/base/hash_tables.h b/base/hash_tables.h
index c2d3ddba158cf77cce5d21dbdb53935b33766cfc..6d1afbdd078e48460de782853b64d16dd3af1eba 100644
--- a/base/hash_tables.h
+++ b/base/hash_tables.h
@@ -7,7 +7,7 @@
 // Deal with the differences between Microsoft and GNU implemenations
 // of hash_map. Allows all platforms to use |base::hash_map| and
 // |base::hash_set|.
-//  eg: 
+//  eg:
 //   base::hash_map<int> my_map;
 //   base::hash_set<int> my_set;
 //
@@ -77,7 +77,21 @@ struct hash<const std::string> {
   size_t operator()(const std::string& s) const {
     return std::tr1::hash<std::string>()(s);
   }
-};  
+};
+
+template<typename T>
+struct hash<T*> {
+  size_t operator()(T* s) const {
+    return std::tr1::hash<T*>()(s);
+  }
+};
+
+template<typename T>
+struct hash<const T*> {
+  size_t operator()(const T* s) const {
+    return std::tr1::hash<const T*>()(s);
+  }
+};
 
 }