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

base/logging_win.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_WIN_H_
 #define BASE_LOGGING_WIN_H_
 
 #include <stddef.h>
 
+#include <memory>
 #include <string>
 
 #include "base/base_export.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/win/event_trace_provider.h"
 
 namespace base {
 template <typename Type>
 struct StaticMemorySingletonTraits;
@@ skipping 30 matching lines @@
   //  the zero-terminated UTF8 message text.
   LOG_MESSAGE_FULL = 12,
 };
 
 // Trace provider class to drive log control and transport
 // with Event Tracing for Windows.
 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();
 
  protected:
   // Overridden to manipulate the log level on ETW control callbacks.
   void OnEventsEnabled() override;
   void OnEventsDisabled() override;
 
  private:
   LogEventProvider();
+  ~LogEventProvider() override;
 
+  class WinLogMessageHandler : LogMessageHandler {
+   public:
+    bool OnMessage(logging::LogSeverity severity,
+                   const char* file,
+                   int line,
+                   size_t message_start,
+                   const std::string& str) override;
+  };
+  std::unique_ptr<WinLogMessageHandler> log_handler_;
   // The log severity prior to OnEventsEnabled,
   // restored in OnEventsDisabled.
   logging::LogSeverity old_log_level_;
 
   friend struct base::StaticMemorySingletonTraits<LogEventProvider>;
   DISALLOW_COPY_AND_ASSIGN(LogEventProvider);
 };
 
 }  // namespace logging
 
 #endif  // BASE_LOGGING_WIN_H_