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

tools/perf/benchmarks/jsgamebench.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 Facebook's JSGameBench benchmark."""
 
 import os
 
 from telemetry import test
 from telemetry.page import page_measurement
 from telemetry.page import page_set
 
 
-class JsgamebenchMeasurement(page_measurement.PageMeasurement):
+class _JsgamebenchMeasurement(page_measurement.PageMeasurement):
   def MeasurePage(self, _, tab, results):
     tab.ExecuteJavaScript('UI.call({}, "perftest")')
     tab.WaitForJavaScriptExpression(
         'document.getElementById("perfscore0") != null', 1200)
     js_get_results = 'document.getElementById("perfscore0").innerHTML'
     result = int(tab.EvaluateJavaScript(js_get_results))
     results.Add('Score', 'score (bigger is better)', result)
 
 
 class Jsgamebench(test.Test):
   """Counts how many animating sprites can move around on the screen at once."""
-  test = JsgamebenchMeasurement
+  test = _JsgamebenchMeasurement
 
   def CreatePageSet(self, options):
     return page_set.PageSet.FromDict({
         'archive_data_file': '../data/jsgamebench.json',
         'pages': [
           { 'url': 'http://localhost/' }
           ]
         }, os.path.dirname(__file__))