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 4a9e061a00a94cdb55701d37ebe20d12e894aca1..e154c29312f7a4d5062c9e2a80f8f06d6d8f1784 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.h
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.h
@@ -33,6 +33,9 @@ class RapporService;
 
 namespace page_load_metrics {
 
+// Returns true if the given URL matches a Google CAPTCHA page.
+bool IsGoogleCaptcha(const GURL& url);
+
 // These constants are for keeping the tests in sync.
 const char kHistogramNameFirstLayout[] =
     "PageLoad.Timing2.NavigationToFirstLayout";
@@ -158,6 +161,16 @@ enum InternalErrorLoadEvent {
   ERR_LAST_ENTRY
 };
 
+// Values of the UMA GoogleCaptcha.Event histogram.
+enum GoogleCaptchaEvent {
+  // A Google CAPTCHA page was shown to the user.
+  GOOGLE_CAPTCHA_SHOWN,
+  // A Google CAPTCHA page was solved by the user.
+  GOOGLE_CAPTCHA_SOLVED,
+  // Add new values before this final count.
+  GOOGLE_CAPTCHA_EVENT_BOUNDARY,
+};
+
 // This class tracks a given page load, starting from navigation start /
 // provisional load, until a new navigation commits or the navigation fails. It
 // also records RAPPOR/UMA about the page load.
@@ -239,6 +252,8 @@ 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;