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

chrome/browser/page_load_metrics/observers/google_captcha_observer.h

Index: chrome/browser/page_load_metrics/observers/google_captcha_observer.h
diff --git a/chrome/browser/page_load_metrics/observers/google_captcha_observer.h b/chrome/browser/page_load_metrics/observers/google_captcha_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..4b0cfc520445e3a6b95535f8f9a746677437b8b0
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+++ b/chrome/browser/page_load_metrics/observers/google_captcha_observer.h
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+// 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 CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_GOOGLE_CAPTCHA_OBSERVER_H_
+#define CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_GOOGLE_CAPTCHA_OBSERVER_H_
+
+#include "base/macros.h"
+#include "components/page_load_metrics/browser/page_load_metrics_observer.h"
+
+namespace google_captcha_observer {
+
+// Returns true if the given URL matches a Google CAPTCHA page.
+bool IsGoogleCaptcha(const GURL& url);
+
+class GoogleCaptchaObserver
+    : public page_load_metrics::PageLoadMetricsObserver {
+ public:
+  explicit GoogleCaptchaObserver(
+      page_load_metrics::PageLoadMetricsObservable* metrics);
+
+  // page_load_metrics::PageLoadMetricsObserver implementation:
+  void OnCommit(content::NavigationHandle* navigation_handle) override;
+  void OnRedirect(content::NavigationHandle* navigation_handle) override;
+  void OnPageLoadMetricsGoingAway() override;
+
+ private:
+  page_load_metrics::PageLoadMetricsObservable* const metrics_;
+  DISALLOW_COPY_AND_ASSIGN(GoogleCaptchaObserver);
+
+};
+
+}  // namespace google_captcha_observer
+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_GOOGLE_CAPTCHA_OBSERVER_H_