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

+// 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);

[Bryan McQuade, 2015/11/16 18:58:55]

re: removing the namespace, could we make this a static method on the
GoogleCaptchaObserver class? and then you can put GoogleCaptchaObserver in the
page_load_metrics namespace. FromGWSObserver should probably also be in
page_load_metrics. I can fix that in a follow up change.

[Charlie Harrison, 2015/11/16 19:12:38]

There was a discussion about this in the original observers CL that
page_load_metrics namespace should only be used in the component. I would be
happy to go against that advice, but we could also have a solution that adds a
special namespace for observer / chrome.

+
+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

[Charlie Harrison, 2015/11/16 19:12:38]

nit: space after }. I just tested git cl format and it doesn't detect this.
Let's just add it here to be consistent.

+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_GOOGLE_CAPTCHA_OBSERVER_H_