Refactor BenchmarkResult.Add to take enum for data_type

tools/perf/metrics/histogram.py

 # Copyright 2013 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 metrics import histogram_util
+from telemetry.page import result_data_type
 
 BROWSER_HISTOGRAM = 'browser_histogram'
 RENDERER_HISTOGRAM = 'renderer_histogram'
 
 class HistogramMetric(object):
   def __init__(self, histogram, histogram_type):
     self.name = histogram['name']
     self.units = histogram['units']
     self.histogram_type = histogram_type
     self._start_values = dict()
 
   def Start(self, page, tab):
     """Get the starting value for the histogram. This value will then be
     subtracted from the actual measurement."""
     data = self._GetHistogramFromDomAutomation(tab)
     if data:
       self._start_values[page.url + self.name] = data
 
   def GetValue(self, page, tab, results):
     data = self._GetHistogramFromDomAutomation(tab)
     if not data:
       return
     new_histogram = histogram_util.SubtractHistogram(
         data, self._start_values[page.url + self.name])
     results.Add(self.name, self.units, new_histogram,
-                data_type='unimportant-histogram')
+                data_type=result_data_type.UNIMPORTANT_HISTOGRAM)
 
   @property
   def histogram_function(self):
     if self.histogram_type == BROWSER_HISTOGRAM:
       return 'getBrowserHistogram'
     return 'getHistogram'
 
   def _GetHistogramFromDomAutomation(self, tab):
     return histogram_util.GetHistogramFromDomAutomation(
         self.histogram_function, self.name, tab)