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

base/logging.h

Index: base/logging.h
diff --git a/base/logging.h b/base/logging.h
index 08189b6114bc020f10905d83e4165bdca67126a1..e927d1daf737e9f168aef5dcc3362eee268611fb 100644
--- a/base/logging.h
+++ b/base/logging.h
@@ -279,14 +279,35 @@ BASE_EXPORT void SetShowErrorDialogs(bool enable_dialogs);
 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
+// Derive the LogMessageHandler that gets passed every log message before

[grt (UTC plus 2), 2016/08/01 21:17:44]

Please review the style guide section on comments and rewrite this.

[wychen, 2016/08/01 23:11:03]

Done.

 // 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.
-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();
+class BASE_EXPORT LogMessageHandler {
+ public:
+  // Returns true to signal that it handled the message and the message
+  // should not be sent to other log destinations, including other handlers
+  // added before the current one.
+  virtual bool OnMessage(int severity, const char* file, int line,
+      size_t message_start, const std::string& str) = 0;
+  virtual ~LogMessageHandler();

[grt (UTC plus 2), 2016/08/01 21:17:44]

Move up; ctors and dtors precede other methods.

[wychen, 2016/08/01 23:11:04]

Done.

+ protected:
+  LogMessageHandler();
+};
+
+BASE_EXPORT size_t LogMessageHandlerCountForTesting();

[grt (UTC plus 2), 2016/08/01 21:17:44]

If this is only used by base_unittests, it should not be exported. Same below.

[wychen, 2016/08/01 23:11:04]

If I don't export it, component build would fail.

[grt (UTC plus 2), 2016/08/02 07:25:46]

Meh. I didn't realize base_unittests linked to base.dll rather than pulling in
the sources directly. Oh well.

+
+// Derive the LogMessageListener that gets passed every log message before
+// it's sent to LogMessageHandler. If hijacking message is not
+// needed, use this one instead of LogMessageHandler.
+class BASE_EXPORT LogMessageListener {
+ public:
+  virtual void OnMessage(int severity, const char* file, int line,
+      size_t message_start, const std::string& str) = 0;
+  virtual ~LogMessageListener();
+ protected:
+  LogMessageListener();
+};
+
+BASE_EXPORT size_t LogMessageListenerCountForTesting();
 
 typedef int LogSeverity;
 const LogSeverity LOG_VERBOSE = -1;  // This is level 1 verbosity