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

base/logging.h

 // Copyright (c) 2012 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_LOGGING_H_
 #define BASE_LOGGING_H_
 
 #include <stddef.h>
 
 #include <cassert>
@@ skipping 264 matching lines @@
 // Sets the Log Assert Handler that will be used to notify of check failures.
 // The default handler shows a dialog box and then terminate the process,
 // however clients can use this function to override with their own handling
 // (e.g. a silent one for Unit Tests)
 typedef void (*LogAssertHandlerFunction)(const std::string& str);
 BASE_EXPORT void SetLogAssertHandler(LogAssertHandlerFunction handler);
 
 // Sets the Log Message Handler that gets passed every log message before
 // it's sent to other log destinations (if any).
 // Returns true to signal that it handled the message and the message
-// should not be sent to other log destinations.
+// should not be sent to other log destinations, including other handlers
+// below the current one in the stack.
 typedef bool (*LogMessageHandlerFunction)(int severity,
     const char* file, int line, size_t message_start, const std::string& str);
-BASE_EXPORT void SetLogMessageHandler(LogMessageHandlerFunction handler);
-BASE_EXPORT LogMessageHandlerFunction GetLogMessageHandler();
+BASE_EXPORT void PushLogMessageHandler(LogMessageHandlerFunction handler);
+// When popping, GetTopLogMessageHandler() is supposed to be |expected|.
+BASE_EXPORT void PopLogMessageHandler(LogMessageHandlerFunction expected);
+BASE_EXPORT LogMessageHandlerFunction GetTopLogMessageHandler();
+
+// Sets the Log Message Listener that gets passed every log message before
+// it's sent to LogMessageHandlerFunctions. If hijacking message is not
+// needed, use this one instead of LogMessageHandlerFunction.
+typedef void (*LogMessageListenerFunction)(int severity,
+    const char* file, int line, size_t message_start, const std::string& str);
+
+class BASE_EXPORT ScopedLogMessageListener {
+ public:
+  ScopedLogMessageListener(LogMessageListenerFunction listener);

[wychen, 2016/07/09 21:21:19]

explicit?

[wychen, 2016/07/18 15:44:12]

Done.

+  ~ScopedLogMessageListener();
+ private:
+  LogMessageListenerFunction listener_;
+};
+
+BASE_EXPORT void AddLogMessageListener(LogMessageListenerFunction listener);
+BASE_EXPORT void RemoveLogMessageListener(LogMessageListenerFunction listener);
 
 typedef int LogSeverity;
 const LogSeverity LOG_VERBOSE = -1;  // This is level 1 verbosity
 // Note: the log severities are used to index into the array of names,
 // see log_severity_names.
 const LogSeverity LOG_INFO = 0;
 const LogSeverity LOG_WARNING = 1;
 const LogSeverity LOG_ERROR = 2;
 const LogSeverity LOG_FATAL = 3;
 const LogSeverity LOG_NUM_SEVERITIES = 4;
@@ skipping 688 matching lines @@
 #elif NOTIMPLEMENTED_POLICY == 5
 #define NOTIMPLEMENTED() do {\
   static bool logged_once = false;\
   LOG_IF(ERROR, !logged_once) << NOTIMPLEMENTED_MSG;\
   logged_once = true;\
 } while(0);\
 EAT_STREAM_PARAMETERS
 #endif
 
 #endif  // BASE_LOGGING_H_