Log First User Interaction in Page Load Metrics

content/browser/renderer_host/input/render_widget_host_latency_tracker.cc

Index: content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
diff --git a/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc b/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
index b0ba89f77e5ae0e26ce0dd96ebd2b16d9a6150d8..1baa04c1f0ed020805226614ab1709947c292212 100644
--- a/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
+++ b/content/browser/renderer_host/input/render_widget_host_latency_tracker.cc
@@ -305,6 +305,11 @@ void RenderWidgetHostLatencyTracker::OnInputEvent(
     const blink::WebInputEvent& event,
     LatencyInfo* latency) {
   DCHECK(latency);
+
+  for (size_t i = 0; i < input_event_callbacks_.size(); ++i) {
+    input_event_callbacks_[i].Run(event);
+  }
+
   if (latency->FindLatency(ui::INPUT_EVENT_LATENCY_BEGIN_RWH_COMPONENT,
                            latency_component_id_, NULL)) {
     return;
@@ -470,4 +475,19 @@ void RenderWidgetHostLatencyTracker::OnFrameSwapped(
                                  latency);
 }
 
+void RenderWidgetHostLatencyTracker::AddInputEventCallback(
+    const InputEventCallback& callback) {
+  input_event_callbacks_.push_back(callback);
+}
+
+void RenderWidgetHostLatencyTracker::RemoveInputEventCallback(
+    const InputEventCallback& callback) {
+  for (size_t i = 0; i < input_event_callbacks_.size(); ++i) {
+    if (input_event_callbacks_[i].Equals(callback)) {
+      input_event_callbacks_.erase(input_event_callbacks_.begin() + i);
+      return;
+    }
+  }
+}
+
 }  // namespace content