Add UMA to count the number of Google CAPTCHA pages shown and solved by users.

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 3cc08830636be60471e40c7f140d8f31eb3c2d0a..c9685b6321f519e106e10798308104b4478a96fb 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.h
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.h
@@ -197,6 +197,7 @@ class PageLoadTracker {
                   PageLoadMetricsEmbedderInterface* embedder_interface,
                   base::ObserverList<PageLoadMetricsObserver, true>* observers);
   ~PageLoadTracker();
+  void Redirect(content::NavigationHandle* navigation_handle);
   void Commit(content::NavigationHandle* navigation_handle);
   void WebContentsHidden();
   void WebContentsShown();
@@ -265,6 +266,8 @@ class MetricsWebContentsObserver
       content::NavigationHandle* navigation_handle) override;
   void DidFinishNavigation(
       content::NavigationHandle* navigation_handle) override;
+  void DidRedirectNavigation(
+      content::NavigationHandle* navigation_handle) override;
 
   void WasShown() override;
   void WasHidden() override;