Add Histogram functionality.

tools/chrome_proxy/webdriver/common.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 argparse
 import json
 import os
 import re
 import socket
 import shlex
@@ skipping 94 matching lines @@
       # Build a dict of flags mapped to the whole argument.
       original_args = {}
       for arg in self._chrome_args:
           original_args[GetDictKey(arg)] = arg
       # Override flags given in code with any command line arguments.
       for override_arg in shlex.split(self._flags.browser_args[0]):
         arg_key = GetDictKey(override_arg)
         if arg_key in original_args:
           self._chrome_args.remove(original_args[arg_key])
         self._chrome_args.add(override_arg)
+    # Always add the flag that allows histograms to be queried in javascript.
+    self._chrome_args.add('--enable-stats-collection-bindings')
 
   def _StartDriver(self):
     """Parses the flags to pass to Chromium, then starts the ChromeDriver.
 
     If running Android, the Android package name is passed to ChromeDriver here.
     """
     self._OverrideChromeArgs()
     capabilities = {
       'loggingPrefs': {'performance': 'INFO'},
       'chromeOptions': {
@@ skipping 121 matching lines @@
     Behavior is analogous to 'function(){ return <script> }();'
 
     Args:
       script: A string of Javascript code.
       timeout: Timeout for the Javascript code to return in seconds.
     Returns:
       A string of the verbatim output from the Javascript execution.
     """
     return self.ExecuteJavascript("return " + script, timeout)
 
+  def GetHistogram(self, histogram):
+    js_query = 'statsCollectionController.getBrowserHistogram("%s")' % histogram
+    string_response = self.ExecuteJavascriptStatement(js_query)
+    return json.loads(string_response)
+
   def GetPerformanceLogs(self, method_filter=r'Network\.responseReceived'):
     """Returns all logged Performance events from Chrome.
 
     Args:
       method_filter: A regex expression to match the method of logged events
         against. Only logs who's method matches the regex will be returned.
     Returns:
       Performance logs as a list of dicts, since the last time this function was
       called.
     """
@@ skipping 128 matching lines @@
     """
     sys.stderr.write("**************************************\n")
     sys.stderr.write("**************************************\n")
     sys.stderr.write("**                                  **\n")
     sys.stderr.write("**          TEST FAILURE            **\n")
     sys.stderr.write("**                                  **\n")
     sys.stderr.write("**************************************\n")
     sys.stderr.write("**************************************\n")
     sys.stderr.write(msg, '\n')
     sys.exit(1)