Mirror syncfs log to console and WebUI, with LogSeverity support.

chrome/browser/sync_file_system/logger.h

 // Copyright 2013 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 CHROME_BROWSER_SYNC_FILE_SYSTEM_LOGGER_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_LOGGER_H_
 
 #include <string>
 #include <vector>
 
+#include "base/logging.h"
 #include "chrome/browser/google_apis/event_logger.h"
 
 namespace sync_file_system {
 // Originally wanted to use 'logging' here, but it conflicts with
 // base/logging.h, and breaks DCHECK() and friends.
 namespace util {
 
 // Logs a message using printf format.
 // This function can be called from any thread.
-void Log(const char* format, ...) PRINTF_FORMAT(1, 2);
+void Log(logging::LogSeverity level, const char* format, ...)
+    PRINTF_FORMAT(2, 3);
+
+// Convinience function so c_str() doesn't always have to be called on strings.
+void Log(logging::LogSeverity level, std::string& format, ...);
 
 // Returns the log history.
 // This function can be called from any thread.
 std::vector<google_apis::EventLogger::Event> GetLogHistory();
 
 }  // namespace util
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_LOGGER_H_