Add desktop engagement metrics.

chrome/browser/metrics/desktop_engagement/chrome_visibility_observer_browsertest.cc

+// Copyright 2016 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.
+
+#include "chrome/browser/metrics/desktop_engagement/chrome_visibility_observer.h"
+
+#include "base/memory/singleton.h"
+#include "chrome/browser/chrome_notification_types.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_list.h"
+#include "chrome/test/base/in_process_browser_test.h"
+#include "chrome/test/base/ui_test_utils.h"
+#include "content/public/browser/notification_service.h"
+#include "content/public/test/test_utils.h"
+
+// Mock class for |ChromeVisibilityObserver| for testing.
+class MockChromeVisibilityObserver : public metrics::ChromeVisibilityObserver {
+ public:
+  MockChromeVisibilityObserver() : is_active_(false) {}
+
+  bool IsActive() const { return is_active_; }

[Alexei Svitkine (slow), 2016/07/28 18:37:22]

is_active()

[gayane -on leave until 09-2017, 2016/07/28 21:21:34]

Done.

+
+ private:
+  void SendVisibilityChangeEvent(bool active) override { is_active_ = active; }
+
+  bool is_active_;
+
+  DISALLOW_COPY_AND_ASSIGN(MockChromeVisibilityObserver);
+};
+
+class ChromeVisibilityObserverBrowserTest : public InProcessBrowserTest {};
+
+IN_PROC_BROWSER_TEST_F(ChromeVisibilityObserverBrowserTest, VisibilityTest) {
+  MockChromeVisibilityObserver observer;
+
+  EXPECT_FALSE(observer.IsActive());
+  Browser* new_browser = CreateBrowser(browser()->profile());
+  EXPECT_TRUE(observer.IsActive());
+
+  Browser* incognito_browser = CreateIncognitoBrowser();
+  EXPECT_TRUE(observer.IsActive());
+
+  CloseBrowserSynchronously(incognito_browser);
+  EXPECT_TRUE(observer.IsActive());
+
+  CloseBrowserSynchronously(new_browser);
+  CloseBrowserSynchronously(browser());
+  EXPECT_FALSE(observer.IsActive());
+}