[SyncFS] Add TaskLog tab on chrome://syncfs-internals

chrome/browser/sync_file_system/task_logger.cc

 // Copyright 2014 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.
 
 #include "chrome/browser/sync_file_system/task_logger.h"
 
 #include "base/stl_util.h"
 
 namespace sync_file_system {
 
 namespace {
 const size_t kMaxLogSize = 500;
 }  // namespace
 
 typedef TaskLogger::TaskLog TaskLog;
 
 TaskLogger::TaskLog::TaskLog() {}
 TaskLogger::TaskLog::~TaskLog() {}
 
 TaskLogger::TaskLogger() {}
 
 TaskLogger::~TaskLogger() {
   ClearLog();
 }
 
 void TaskLogger::RecordLog(scoped_ptr<TaskLog> log) {
+  if (!log)
+    return;
+
   if (log_history_.size() >= kMaxLogSize) {
     delete log_history_.front();
     log_history_.pop_front();
   }
 
   log_history_.push_back(log.release());
 
   FOR_EACH_OBSERVER(Observer, observers_,
                     OnLogRecorded(*log_history_.back()));
 }
 
 void TaskLogger::ClearLog() {
   STLDeleteContainerPointers(log_history_.begin(), log_history_.end());
   log_history_.clear();
 }
 
 void TaskLogger::AddObserver(Observer* observer) {
   observers_.AddObserver(observer);
 }
 
 void TaskLogger::RemoveObserver(Observer* observer) {
   observers_.RemoveObserver(observer);
 }
 
 const TaskLogger::LogList& TaskLogger::GetLog() const {
   return log_history_;
 }
 
 }  // namespace sync_file_system