Log First User Interaction in Page Load Metrics

content/browser/renderer_host/input/render_widget_host_latency_tracker.h

Index: content/browser/renderer_host/input/render_widget_host_latency_tracker.h
diff --git a/content/browser/renderer_host/input/render_widget_host_latency_tracker.h b/content/browser/renderer_host/input/render_widget_host_latency_tracker.h
index 633e4e878da43bb4097739ec8f934ec3c227ffd9..0363e31d8d264c76a2193f884b38e1c7a5b3fdb5 100644
--- a/content/browser/renderer_host/input/render_widget_host_latency_tracker.h
+++ b/content/browser/renderer_host/input/render_widget_host_latency_tracker.h
@@ -60,11 +60,18 @@ class CONTENT_EXPORT RenderWidgetHostLatencyTracker {
   // subsystem.
   int64_t latency_component_id() const { return latency_component_id_; }
 
+  // Add/remove a callback that can handle input events routed to latency
+  // tracker.
+  typedef base::Callback<bool(const blink::WebInputEvent&)> InputEventCallback;
+  void AddInputEventCallback(const InputEventCallback& callback);
+  void RemoveInputEventCallback(const InputEventCallback& callback);
+
  private:
   int64_t last_event_id_;
   int64_t latency_component_id_;
   float device_scale_factor_;
   bool has_seen_first_gesture_scroll_update_;
+  std::vector<InputEventCallback> input_event_callbacks_;

[Bryan McQuade, 2016/05/25 21:32:30]

can you use base::ObserverList here? the comments note that it's safer to use
than vector<> since clients can safely remove themselves as observers during
iteration, whereas that doesn't work correctly with vector<>s.

 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostLatencyTracker);
 };