Add UMA stat to track home button and page prefs

chrome/browser/prefs/pref_metrics_service.h

+// Copyright (c) 2013 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_PREFS_PREF_METRICS_SERVICE_H_
+#define CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_
+
+#include "base/memory/singleton.h"
+#include "chrome/browser/profiles/profile.h"
+#include "components/browser_context_keyed_service/browser_context_keyed_service.h"
+#include "components/browser_context_keyed_service/browser_context_keyed_service_factory.h"
+
+// PrefMetricsService is responsible for recording prefs-related UMA stats.
+class PrefMetricsService : public BrowserContextKeyedService {
+ public:
+  explicit PrefMetricsService(Profile* profile);
+  virtual ~PrefMetricsService();
+
+  class Factory : public BrowserContextKeyedServiceFactory {
+   public:
+    static Factory* GetInstance();
+    static PrefMetricsService* GetForProfile(Profile* profile);
+   private:
+    friend struct DefaultSingletonTraits<Factory>;
+
+    Factory();
+    virtual ~Factory();
+
+    // BrowserContextKeyedServiceFactory implementation
+    virtual BrowserContextKeyedService* BuildServiceInstanceFor(
+        content::BrowserContext* profile) const OVERRIDE;
+    virtual bool ServiceIsCreatedWithBrowserContext() const OVERRIDE;
+    virtual bool ServiceIsNULLWhileTesting() const OVERRIDE;
+    virtual content::BrowserContext* GetBrowserContextToUse(
+        content::BrowserContext* context) const OVERRIDE;
+  };
+ private:
+  // Record prefs state on browser context creation.
+  void RecordLaunchPrefs();
+
+  Profile* profile_;
+};
+
+#endif  // CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_