Allow multiple logging::LogMessage{Handler,Listener}s

base/test/mock_log.h

 // Copyright 2015 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_TEST_MOCK_LOG_H_
 #define BASE_TEST_MOCK_LOG_H_
 
 #include <stddef.h>
 
 #include <string>
@@ skipping 70 matching lines @@
   // Called once for each message.
   static bool LogMessageHandler(int severity,
                                 const char* file,
                                 int line,
                                 size_t message_start,
                                 const std::string& str);
 
   // True if this object is currently capturing logs.
   bool is_capturing_logs_;
 
-  // The previous handler to restore when the MockLog is destroyed.
-  logging::LogMessageHandlerFunction previous_handler_;
-
   DISALLOW_COPY_AND_ASSIGN(MockLog);
 };
 
 }  // namespace test
 }  // namespace base
 
 #endif  // BASE_TEST_MOCK_LOG_H_