Refactor BenchmarkResult.Add to take enum for data_type

tools/telemetry/telemetry/page/page_measurement_value.py

Index: tools/telemetry/telemetry/page/page_measurement_value.py
===================================================================
--- tools/telemetry/telemetry/page/page_measurement_value.py	(revision 222891)
+++ tools/telemetry/telemetry/page/page_measurement_value.py	(working copy)
@@ -1,8 +1,14 @@
 # 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.
-from telemetry.page import perf_tests_helper
 
+from telemetry.core import util
+
+# Get build scripts into our path.
+util.AddDirToPythonPath(util.GetChromiumSrcDir(), 'build', 'util', 'lib')
+from common import perf_result_data_type # pylint: disable=F0401
+from common import perf_tests_results_helper  # pylint: disable=F0401
+
 def _Mean(l):
   return float(sum(l)) / len(l) if len(l) > 0 else 0.0
 
@@ -23,8 +29,9 @@
 
   @property
   def output_value(self):
-    if 'histogram' in self.data_type:
-      (mean, _) = perf_tests_helper.GeomMeanAndStdDevFromHistogram(self.value)
+    if perf_result_data_type.IsHistogram(self.data_type):
+      (mean, _) = (perf_tests_results_helper
+                   .GeomMeanAndStdDevFromHistogram(self.value))
       return mean
     elif isinstance(self.value, list):
       return _Mean(self.value)