Hook up PA_LOG() logs to chrome://proximity-auth WebUI.

components/proximity_auth/logging/log_buffer.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 COMPONENTS_PROXIMITY_AUTH_LOGGING_LOG_BUFFER_H
 #define COMPONENTS_PROXIMITY_AUTH_LOGGING_LOG_BUFFER_H
 
 #include <list>
 
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "base/time/time.h"
 
 namespace proximity_auth {
 
 // Contains logs specific to the Proximity Auth. This buffer has a maximum size
 // and will discard entries in FIFO order.
 // Call LogBuffer::GetInstance() to get the global LogBuffer instance.
 class LogBuffer {
  public:
   // Represents a single log entry in the log buffer.
   struct LogMessage {
     const std::string text;
     const base::Time time;
     const std::string file;
     const int line;
     const logging::LogSeverity severity;
 
     LogMessage(const std::string& text,
                const base::Time& time,
                const std::string& file,
                int line,
                logging::LogSeverity severity);
   };
 
+  class Observer {
+   public:
+    // Called when a new message is added to the log buffer.
+    virtual void OnLogMessageAdded(const LogMessage& log_message) = 0;
+
+    // Called when all messages in the log buffer are cleared.
+    virtual void OnLogBufferCleared() = 0;
+  };
+
   LogBuffer();
   ~LogBuffer();
 
   // Returns the global instance.
   static LogBuffer* GetInstance();
 
+  // Adds and removes log buffer observers.
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
   // Adds a new log message to the buffer. If the number of log messages exceeds
   // the maximum, then the earliest added log will be removed.
   void AddLogMessage(const LogMessage& log_message);
 
   // Clears all logs in the buffer.
   void Clear();
 
   // Returns the maximum number of logs that can be stored.
   size_t MaxBufferSize() const;
 
   // Returns the list logs in the buffer, sorted chronologically.
   const std::list<LogMessage>* logs() { return &log_messages_; }
 
  private:
   // The messages currently in the buffer.
   std::list<LogMessage> log_messages_;
 
+  // List of observers.
+  ObserverList<Observer> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(LogBuffer);
 };
 
 }  // namespace proximity_auth
 
 #endif  // COMPONENTS_PROXIMITY_AUTH_LOGGING_LOG_BUFFER_H