[perf] Add a SceneDisplayLag event when we miss vsyncs

shell/common/rasterizer.cc

@@ -242,6 +242,7 @@ RasterStatus Rasterizer::DoDraw(
   }
 
   FrameTiming timing;
+  const fml::TimePoint frame_target_time = layer_tree->target_time();
   timing.Set(FrameTiming::kBuildStart, layer_tree->build_start());
   timing.Set(FrameTiming::kBuildFinish, layer_tree->build_finish());
   timing.Set(FrameTiming::kRasterStart, fml::TimePoint::Now());
@@ -271,6 +272,32 @@ RasterStatus Rasterizer::DoDraw(
   timing.Set(FrameTiming::kRasterFinish, raster_finish_time);
   delegate_.OnFrameRasterized(timing);
 
+  if (raster_finish_time > frame_target_time) {
+    fml::TimePoint latest_frame_target_time =
+        delegate_.GetLatestFrameTargetTime();
+    const auto frame_budget_millis = delegate_.GetFrameBudget().count();
+    if (latest_frame_target_time < raster_finish_time) {
+      latest_frame_target_time =
+          latest_frame_target_time +
+          fml::TimeDelta::FromMillisecondsF(frame_budget_millis);
+    }
+    const auto frame_lag =
+        (latest_frame_target_time - frame_target_time).ToMillisecondsF();
+    const int vsync_transitions_missed = round(frame_lag / frame_budget_millis);
+    fml::tracing::TraceEventAsyncComplete(
+        "flutter",                    // category
+        "SceneDisplayLag",            // name
+        raster_finish_time,           // begin_time
+        latest_frame_target_time,     // end_time
+        "frame_target_time",          // arg_key_1
+        frame_target_time,            // arg_val_1
+        "current_frame_target_time",  // arg_key_2
+        latest_frame_target_time,     // arg_val_2
+        "vsync_transitions_missed",   // arg_key_3
+        vsync_transitions_missed      // arg_val_3
+    );
+  }
+
   // Pipeline pressure is applied from a couple of places:
   // rasterizer: When there are more items as of the time of Consume.
   // animator (via shell): Frame gets produces every vsync.