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

tools/perf/metrics/gpu_rendering_stats.py

Index: tools/perf/metrics/gpu_rendering_stats.py
diff --git a/tools/perf/metrics/gpu_rendering_stats.py b/tools/perf/metrics/gpu_rendering_stats.py
index 9af9f9e1bf61a115df05b8dbbba2596ef67f7520..42ad485b196f3de3671a12a490db1670e4669ac1 100644
--- a/tools/perf/metrics/gpu_rendering_stats.py
+++ b/tools/perf/metrics/gpu_rendering_stats.py
@@ -45,3 +45,10 @@ class GpuRenderingStats(object):
     self.touch_acked_latency = rs.get('totalTouchAckedLatency', 0)
     self.scroll_update_count = rs.get('scrollUpdateCount', 0)
     self.scroll_update_latency = rs.get('totalScrollUpdateLatency', 0)
+    self.impl_to_main_touch_event_count = rs.get('implToMainTouchEventCount', 0)
+    self.total_impl_to_main_touch_event_latency = rs.get(
+        'totalImplToMainTouchEventLatency', 0)
+    self.impl_to_main_gesture_scroll_event_count = rs.get(
+        'implToMainGestureScrollEventCount', 0)
+    self.total_impl_to_main_gesture_scroll_event_latency = rs.get(
+        'totalImplToMainGestureScrollEventLatency', 0)