Refactor BenchmarkResult.Add to take enum for data_type

tools/perf/metrics/memory.py

Index: tools/perf/metrics/memory.py
===================================================================
--- tools/perf/metrics/memory.py	(revision 218037)
+++ tools/perf/metrics/memory.py	(working copy)
@@ -6,6 +6,7 @@
 
 from metrics import histogram_util
 from metrics import Metric
+from telemetry.page import result_data_type
 
 _HISTOGRAMS = [
     {'name': 'V8.MemoryExternalFragmentationTotal', 'units': 'percent',
@@ -71,7 +72,7 @@
       if h['name'] not in self._histogram_start:
         continue
       results.Add(h['name'], h['units'], self._histogram_delta[h['name']],
-                  data_type='unimportant-histogram')
+                  data_type=result_data_type.UNIMPORTANT_HISTOGRAM)
 
   def AddSummaryResults(self, results):
     """Add summary (overall) results to the results object."""
@@ -106,7 +107,8 @@
             values.append(stats[value_name_memory])
         if values:
           results.AddSummary(value_name_trace + process_type_trace,
-                             'bytes', sum(values), data_type='unimportant')
+                             'bytes', sum(values),
+                             data_type=result_data_type.UNIMPORTANT_HISTOGRAM)
 
       AddSummary('VM', 'vm_final_size_')
       AddSummary('WorkingSetSize', 'vm_%s_final_size_' % metric)
@@ -123,7 +125,7 @@
     end_commit_charge = self._memory_stats['SystemCommitCharge']
     commit_charge_difference = end_commit_charge - self._start_commit_charge
     results.AddSummary('commit_charge', 'kb', commit_charge_difference,
-                       data_type='unimportant')
+                       data_type=result_data_type.UNIMPORTANT)
     results.AddSummary('processes', 'count', self._memory_stats['ProcessCount'],
-                       data_type='unimportant')
+                       data_type=result_data_type.UNIMPORTANT)