Refactor BenchmarkResult.Add to take enum for data_type

tools/perf/benchmarks/octane.py

Index: tools/perf/benchmarks/octane.py
===================================================================
--- tools/perf/benchmarks/octane.py	(revision 217866)
+++ tools/perf/benchmarks/octane.py	(working copy)
@@ -7,6 +7,7 @@
 from telemetry import test
 from telemetry.core import util
 from telemetry.page import page_measurement
+from telemetry.page import result_data_type
 from telemetry.page import page_set
 
 
@@ -36,9 +37,9 @@
     for key, value in result_dict.iteritems():
       if value == '...':
         continue
-      data_type = 'unimportant'
+      data_type = result_data_type.UNIMPORTANT
       if key == 'score':
-        data_type = 'default'
+        data_type = result_data_type.DEFAULT
       results.Add(key, 'score (bigger is better)', value, data_type=data_type)