Refactor BenchmarkResult.Add to take enum for data_type

tools/perf/benchmarks/dom_perf.py

Index: tools/perf/benchmarks/dom_perf.py
===================================================================
--- tools/perf/benchmarks/dom_perf.py	(revision 217866)
+++ tools/perf/benchmarks/dom_perf.py	(working copy)
@@ -10,8 +10,8 @@
 from telemetry.core import util
 from telemetry.page import page_measurement
 from telemetry.page import page_set
+from telemetry.page import result_data_type
 
-
 def _GeometricMean(values):
   """Compute a rounded geometric mean from an array of values."""
   if not values:
@@ -51,7 +51,8 @@
         # Skip benchmarks that we didn't actually run this time around.
         if len(suite['Benchmarks']) or suite['score']:
           results.Add(SCORE_TRACE_NAME, SCORE_UNIT,
-                      suite['score'], suite['name'], 'unimportant')
+                      suite['score'], suite['name'],
+                      result_data_type.UNIMPORTANT)
     finally:
       tab.EvaluateJavaScript('document.cookie = "__domperf_finished=0"')