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

ui/base/latency_info.h

Index: ui/base/latency_info.h
diff --git a/ui/base/latency_info.h b/ui/base/latency_info.h
index 423182a0379ea382d9b40cda4c231511904750ff..251c2e7aa36176e3db9cb91523f56eb4a09dfaa5 100644
--- a/ui/base/latency_info.h
+++ b/ui/base/latency_info.h
@@ -31,7 +31,11 @@ enum LatencyComponentType {
   INPUT_EVENT_LATENCY_UI_COMPONENT,
   // Timestamp when the event is acked from renderer. This is currently set
   // only for touch events.
-  INPUT_EVENT_LATENCY_ACKED_COMPONENT
+  INPUT_EVENT_LATENCY_ACKED_COMPONENT,
+  // Timestamp when the event is sent from the impl to main renderer thread.
+  INPUT_EVENT_LATENCY_SENT_FROM_IMPL_THREAD_COMPONENT,
+  // Timestamp when the event is received on the main thread.
+  INPUT_EVENT_LATENCY_RECEIVED_ON_MAIN_THREAD_COMPONENT,
 };
 
 struct UI_EXPORT LatencyInfo {