Add telemetry to track the time an event spent waiting for the main thread.

tools/perf/metrics/smoothness.py

Index: tools/perf/metrics/smoothness.py
diff --git a/tools/perf/metrics/smoothness.py b/tools/perf/metrics/smoothness.py
index c4ec7bc57eb529449731f315190bc471a6701b08..455dc3d453b86aedb2a7850b9d9ad29cf2020af2 100644
--- a/tools/perf/metrics/smoothness.py
+++ b/tools/perf/metrics/smoothness.py
@@ -155,3 +155,11 @@ def CalcResults(benchmark_stats, results):
               Average(s.scroll_update_latency, s.scroll_update_count,
                       1000, 3),
               data_type='unimportant')
+  results.Add('average_impl_to_main_touch_event_latency', 'ms',
+              Average(s.total_impl_to_main_touch_event_latency,
+                      s.impl_to_main_touch_event_count, 1000, 3),
+              data_type='unimportant')
+  results.Add('average_impl_to_main_gesture_scroll_event_latency', 'ms',
+              Average(s.total_impl_to_main_gesture_scroll_event_latency,
+                      s.impl_to_main_gesture_scroll_event_count, 1000, 3),
+              data_type='unimportant')