Isolate tests by running AtExit callbacks between them.

base/at_exit.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 BASE_AT_EXIT_H_
 #define BASE_AT_EXIT_H_
 
 #include <stack>
 
 #include "base/basictypes.h"
@@ skipping 48 matching lines @@
     void* param_;
   };
 
   Lock lock_;
   std::stack<CallbackAndParam> stack_;
   AtExitManager* next_manager_;  // Stack of managers to allow shadowing.
 
   DISALLOW_COPY_AND_ASSIGN(AtExitManager);
 };
 
+#if defined(UNIT_TEST)
+class ShadowingAtExitManager : public AtExitManager {
+ public:
+  ShadowingAtExitManager() : AtExitManager(true) {}
+};
+#endif  // defined(UNIT_TEST)
+
 }  // namespace base
 
 #endif  // BASE_AT_EXIT_H_