Log an immediate variant of FirstContentfulPaint.

components/page_load_metrics/browser/page_load_metrics_observer.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_OBSERVER_H_
 #define COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_OBSERVER_H_
 
 #include "base/macros.h"
 #include "components/page_load_metrics/common/page_load_timing.h"
 #include "content/public/browser/navigation_handle.h"
@@ skipping 107 matching lines @@
   // reference to it.
   // Note that this does not get called for same page navigations.
   virtual void OnCommit(content::NavigationHandle* navigation_handle) {}
 
   // OnFailedProvisionalLoad is triggered when a provisional load failed and did
   // not commit. Note that provisional loads that result in downloads or 204s
   // are aborted by the system, and thus considered failed provisional loads.
   virtual void OnFailedProvisionalLoad(
       content::NavigationHandle* navigation_handle) {}
 
+  // OnTimingUpdate is triggered when an updated PageLoadTiming is
+  // available. This method may be called multiple times over the course of the
+  // page load. Note that this is currently an experimental API which may be
+  // removed in the future. Please email loading-dev@chromium.org if you intend
+  // to override this method.
+  virtual void OnTimingUpdate(const PageLoadTiming& timing,
+                              const PageLoadExtraInfo& extra_info) {}
+
   // OnComplete is triggered when we are ready to record metrics for this page
   // load. This will happen some time after commit. The PageLoadTiming struct
   // contains timing data and the PageLoadExtraInfo struct contains other useful
   // data collected over the course of the page load. If the load did not
   // receive any timing information, |timing.IsEmpty()| will be true.
   // After this call, the object will be deleted.
   virtual void OnComplete(const PageLoadTiming& timing,
                           const PageLoadExtraInfo& extra_info) {}
 };
 
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_OBSERVER_H_