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

base/logging_win.h

Index: base/logging_win.h
diff --git a/base/logging_win.h b/base/logging_win.h
index cdde7bb687cbbd524a0b5e412e0a2c6714b06f3f..35ca3d42981f378c6f2255f499d4fd34d5982849 100644
--- a/base/logging_win.h
+++ b/base/logging_win.h
@@ -57,9 +57,6 @@ class BASE_EXPORT LogEventProvider : public base::win::EtwTraceProvider {
  public:
   static LogEventProvider* GetInstance();
 
-  static bool LogMessage(logging::LogSeverity severity, const char* file,
-      int line, size_t message_start, const std::string& str);
-
   static void Initialize(const GUID& provider_name);
   static void Uninitialize();
 
@@ -71,6 +68,15 @@ class BASE_EXPORT LogEventProvider : public base::win::EtwTraceProvider {
  private:
   LogEventProvider();
 
+  class WinLogMessageHandler : LogMessageHandler {
+   public:
+    bool OnMessage(logging::LogSeverity severity,
+                   const char* file,
+                   int line,
+                   size_t message_start,
+                   const std::string& str) override;
+  };
+  static WinLogMessageHandler* log_handler_;
   // The log severity prior to OnEventsEnabled,
   // restored in OnEventsDisabled.
   logging::LogSeverity old_log_level_;