Add a histogram for delay between first paint and client side redirects.

components/page_load_metrics/browser/metrics_web_contents_observer.h

Index: components/page_load_metrics/browser/metrics_web_contents_observer.h
diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer.h b/components/page_load_metrics/browser/metrics_web_contents_observer.h
index dee13cbd092303adb4215e68fe72b96bb8c9f222..2334223f46abbb1460b45f2d6494c1f3239aaab0 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.h
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.h
@@ -135,6 +135,8 @@ class PageLoadTracker {
 
   void OnInputEvent(const blink::WebInputEvent& event);
 
+  void NotifyClientRedirectTo(const PageLoadTracker& destination);
+
   // Returns true if the timing was successfully updated.
   bool UpdateTiming(const PageLoadTiming& timing,
                     const PageLoadMetadata& metadata);
@@ -181,6 +183,8 @@ class PageLoadTracker {
     return url_;
   }
 
+  base::TimeTicks navigation_start() const { return navigation_start_; }
+
   PageLoadExtraInfo ComputePageLoadExtraInfo();
 
  private: