Refactor BenchmarkResult.Add to take enum for data_type

tools/perf/metrics/media.py

Index: tools/perf/metrics/media.py
===================================================================
--- tools/perf/metrics/media.py	(revision 222891)
+++ tools/perf/metrics/media.py	(working copy)
@@ -4,8 +4,12 @@
 import logging
 import os
 
+from telemetry.core import util
 from metrics import Metric
 
+# Get build scripts into our path.
+util.AddDirToPythonPath(util.GetChromiumSrcDir(), 'build', 'util', 'lib')
+from common import perf_result_data_type # pylint: disable=F0401
 
 class MediaMetric(Metric):
   """MediaMetric class injects and calls JS responsible for recording metrics.
@@ -57,7 +61,8 @@
         if m.startswith(metric):
           special_label = m[len(metric):]
           results.Add(trace + special_label, unit, str(metrics[m]),
-                      chart_name=metric, data_type='default')
+                      chart_name=metric,
+                      data_type=perf_result_data_type.DEFAULT)
 
     trace = media_metric['id']
     if not trace: