[SyncFS] Add TaskLogger and wire up it.

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 {
+
+typedef TaskLogger::TaskLog TaskLog;
+
+TaskLogger::TaskLog::TaskLog() {}
+TaskLogger::TaskLog::~TaskLog() {}
+
+TaskLogger::TaskLogger() : log_size_(500) {}
+
+TaskLogger::~TaskLogger() {
+  ClearLog();
+}
+
+void TaskLogger::RecordLog(scoped_ptr<TaskLog> log) {
+  if (log_history_.size() >= log_size_) {
+    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 std::deque<TaskLog*>& TaskLogger::GetLog() const {
+  return log_history_;
+}
+
+}  // namespace sync_file_system