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

components/page_load_metrics/browser/metrics_web_contents_observer.cc

Index: components/page_load_metrics/browser/metrics_web_contents_observer.cc
diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer.cc b/components/page_load_metrics/browser/metrics_web_contents_observer.cc
index 7f304bb4657ed4be237c1eb6f605eeafcb82d6e3..6e2feb758577de6ff83b3cc02179315f5fd6f57c 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.cc
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.cc
@@ -7,6 +7,7 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
+#include "base/metrics/user_metrics.h"
 #include "components/page_load_metrics/browser/page_load_metrics_macros.h"
 #include "components/page_load_metrics/common/page_load_metrics_messages.h"
 #include "components/page_load_metrics/common/page_load_timing.h"
@@ -159,6 +160,11 @@ void PageLoadTracker::Commit(content::NavigationHandle* navigation_handle) {
                     OnCommit(navigation_handle));
 }
 
+void PageLoadTracker::Redirect(content::NavigationHandle* navigation_handle) {
+  FOR_EACH_OBSERVER(PageLoadMetricsObserver, *observers_,
+                    OnRedirect(navigation_handle));
+}
+
 bool PageLoadTracker::UpdateTiming(const PageLoadTiming& new_timing) {
   // Throw away IPCs that are not relevant to the current navigation.
   // Two timing structures cannot refer to the same navigation if they indicate
@@ -471,6 +477,16 @@ void MetricsWebContentsObserver::DidFinishNavigation(
   committed_load_->Commit(navigation_handle);
 }
 
+void MetricsWebContentsObserver::DidRedirectNavigation(
+    content::NavigationHandle* navigation_handle) {
+  if (!navigation_handle->IsInMainFrame())
+    return;
+  auto it = provisional_loads_.find(navigation_handle);
+  if (it == provisional_loads_.end())
+    return;
+  it->second->Redirect(navigation_handle);
+}
+
 void MetricsWebContentsObserver::WasShown() {
   in_foreground_ = true;
   if (committed_load_)