[telemetry] Make single-benchmark measurements protected and undiscoverable.

tools/perf/benchmarks/robohornet_pro.py

 # Copyright (c) 2012 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.
 
 """Runs Microsoft's RoboHornet Pro benchmark."""
 
 import os
 
 from telemetry import test
 from telemetry.page import page_measurement
 from telemetry.page import page_set
 
 
-class RobohornetProMeasurement(page_measurement.PageMeasurement):
+class _RobohornetProMeasurement(page_measurement.PageMeasurement):
   def MeasurePage(self, _, tab, results):
     tab.ExecuteJavaScript('ToggleRoboHornet()')
     tab.WaitForJavaScriptExpression(
         'document.getElementById("results").innerHTML.indexOf("Total") != -1',
         120)
     result = int(tab.EvaluateJavaScript('stopTime - startTime'))
     results.Add('Total', 'ms', result)
 
 
 class RobohornetPro(test.Test):
-  test = RobohornetProMeasurement
+  test = _RobohornetProMeasurement
 
   def CreatePageSet(self, options):
     return page_set.PageSet.FromDict({
         'archive_data_file': '../data/robohornetpro.json',
         # Measurement require use of real Date.now() for measurement.
         'make_javascript_deterministic': False,
         'pages': [
           { 'url':
             'http://ie.microsoft.com/testdrive/performance/robohornetpro/' }
           ]
         }, os.path.abspath(__file__))