Fix the timestamp generation for webrtc native log.

chrome/common/media/webrtc_logging_message_data.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/common/media/webrtc_logging_message_data.h"
+
+#include "base/strings/stringprintf.h"
+
+WebRtcLoggingMessageData::WebRtcLoggingMessageData() {}
+
+WebRtcLoggingMessageData::WebRtcLoggingMessageData(const base::Time& time,
+                                                   const std::string& message)
+    : timestamp(time), message(message) {}
+
+std::string
+WebRtcLoggingMessageData::Format(const base::Time& start_time) const {
+  uint64 interval_ms = (timestamp - start_time).InMilliseconds();
+
+  std::string result = base::StringPrintf("[%03ld:%03ld] %s",
+                                          interval_ms / 1000,
+                                          interval_ms % 1000,
+                                          message.c_str());
+  return result;
+}