Refactor BenchmarkResult.Add to take enum for data_type

tools/perf/measurements/tab_switching.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.
 
 """The tab switching measurement.
 
 This measurement opens pages in different tabs. After all the tabs have opened,
 it cycles through each tab in sequence, and records a histogram of the time
 between when a tab was first requested to be shown, and when it was painted.
 """
 
 from metrics import histogram_util
 from telemetry.core import util
 from telemetry.page import page_measurement
+from telemetry.page import result_data_type
 from telemetry.page import page_runner
 
 # TODO: Revisit this test once multitab support is finalized.
 
 class TabSwitching(page_measurement.PageMeasurement):
   def CustomizeBrowserOptions(self, options):
     options.AppendExtraBrowserArg('--enable-stats-collection-bindings')
     options.AppendExtraBrowserArg('--dom-automation')
 
   def CanRunForPage(self, page):
@@ skipping 30 matching lines @@
       util.WaitFor(_IsDone, 30)
       prev_histogram = histogram_util.GetHistogramFromDomAutomation(
           histogram_type, histogram_name, tab)
 
     last_histogram = histogram_util.GetHistogramFromDomAutomation(
         histogram_type, histogram_name, tab)
     diff_histogram = histogram_util.SubtractHistogram(last_histogram,
         first_histogram)
 
     results.AddSummary(histogram_name, '', diff_histogram,
-        data_type='unimportant-histogram')
+                       data_type=result_data_type.UNIMPORTANT_HISTOGRAM)