Update cpu and memory metric calculation and several small improvements.

chrome/test/media_router/telemetry/benchmarks/pagesets/media_router_page.py

 # Copyright 2016 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.
 
 import os
 import time
+import utils
 
 from telemetry import page
 from telemetry import story
 from telemetry.core import exceptions
 
 
 class CastPage(page.Page):
   """Abstract Cast page for Media Router Telemetry tests."""
 
   def ChooseSink(self, tab, sink_name):
@@ skipping 35 matching lines @@
 
     start_time = time.time()
     while (not verify_func() and
            time.time() - start_time < timeout):
       action_runner.Wait(1)
     if not verify_func():
       raise page.page_test.Failure(error_message)
 
   def _GetDeviceName(self):
     """Gets device name from environment variable RECEIVER_NAME."""
-    if 'RECEIVER_NAME' not in os.environ or not os.environ.get('RECEIVER_NAME'):
+
+    if 'RECEIVER_IP' not in os.environ or not os.environ.get('RECEIVER_IP'):
       raise page.page_test.Failure(
           'Your test machine is not set up correctly, '
-          'RECEIVER_NAME enviroment variable is missing.')
-    return os.environ.get('RECEIVER_NAME')
+          'RECEIVER_IP enviroment variable is missing.')
+    return utils.GetDeviceName(os.environ.get('RECEIVER_IP'))