Addition of first_gesture_scroll_latency

tools/telemetry/telemetry/web_perf/metrics/smoothness.py

Index: tools/telemetry/telemetry/web_perf/metrics/smoothness.py
diff --git a/tools/telemetry/telemetry/web_perf/metrics/smoothness.py b/tools/telemetry/telemetry/web_perf/metrics/smoothness.py
index 6bde6d6bb714ed3c88022d525879b3148bb709fd..0e9f37a5be46fbf09852849954abe969d457a15b 100644
--- a/tools/telemetry/telemetry/web_perf/metrics/smoothness.py
+++ b/tools/telemetry/telemetry/web_perf/metrics/smoothness.py
@@ -22,6 +22,7 @@ class SmoothnessMetric(timeline_based_metric.TimelineBasedMetric):
       [r.GetBounds() for r in interaction_records])
 
     input_event_latency = FlattenList(stats.input_event_latency)
+
     if input_event_latency:
       mean_input_event_latency = statistics.ArithmeticMean(
         input_event_latency)
@@ -34,7 +35,21 @@ class SmoothnessMetric(timeline_based_metric.TimelineBasedMetric):
           results.current_page, 'input_event_latency_discrepancy', 'ms',
           round(input_event_latency_discrepancy, 4)))
 
-    # List of queueing durations.
+    input_start_and_latency_GSU = FlattenList(stats.input_start_and_latency_GSU)

[nduca, 2014/08/01 19:21:26]

specifically should we have tests for the smoothness metric part? or do we not
currently unit test the integration point?

[jdduke (slow), 2014/08/09 01:58:50]

Hmm, looks like the smoothness metric lacks unit tests.  Coverage would be nice,
maybe in a follow-up patch?

+
+    if input_start_and_latency_GSU:
+      first_GSU_event = min(
+          input_start_and_latency_GSU,
+          key = lambda event:event.start_time)
+
+      results.AddValue(scalar.ScalarValue(
+           results.current_page,
+           'first_gesture_scroll_latency',
+           'ms',
+           round(first_GSU_event.latency, 4)))
+
+    # List of queueing durations
+
     frame_queueing_durations = FlattenList(stats.frame_queueing_durations)
     if frame_queueing_durations:
       results.AddValue(list_of_scalar_values.ListOfScalarValues(