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

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 "components/page_load_metrics/common/page_load_timing.h"
 #include "content/public/browser/navigation_handle.h"
 
@@ skipping 22 matching lines @@
 // OnCommit to be fired without a subsequent OnComplete (i.e. if an error
 // occurs or we don't have any metrics to log). PageLoadMetricsObservers are
 // required to stop observing (call PageLoadMetricsObservable::RemoveObserver)
 // some time before the OnPageLoadMetricsGoingAway trigger finishes. If this
 // class is destroyed before the PageLoadMetricsObservable, it should call
 // RemoveObserver in its destructor.
 class PageLoadMetricsObserver {
  public:
   virtual ~PageLoadMetricsObserver() {}
 
+  // OnRedirect is triggered when a page load redirects to another URL.
+  // The navigation handle holds relevant data for the navigation, but will
+  // be destroyed soon after this call. Don't hold a reference to it.
+  virtual void OnRedirect(content::NavigationHandle* navigation_handle) {}
+
   // OnCommit is triggered when a page load commits, i.e. when we receive the
   // first data for the request. The navigation handle holds relevant data for
   // the navigation, but will be destroyed soon after this call. Don't hold a
   // reference to it.
   virtual void OnCommit(content::NavigationHandle* navigation_handle) {}
 
   // OnComplete is triggered when we are ready to record metrics for this page
   // load. This will happen some time after commit, and will be triggered as
   // long as we've received some data about the page load. The
   // PageLoadTiming struct contains timing data and the PageLoadExtraInfo struct
@@ skipping 12 matching lines @@
 class PageLoadMetricsObservable {
  public:
   virtual ~PageLoadMetricsObservable() {}
   virtual void AddObserver(PageLoadMetricsObserver* observer) = 0;
   virtual void RemoveObserver(PageLoadMetricsObserver* observer) = 0;
 };
 
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_OBSERVER_H_