Add DelayNavigationThrottle

chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.h

+// Copyright 2017 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_EXPERIMENTS_DELAY_NAVIGATION_THROTTLE_H_
+#define CHROME_BROWSER_PAGE_LOAD_METRICS_EXPERIMENTS_DELAY_NAVIGATION_THROTTLE_H_
+
+#include <memory>
+
+#include "base/feature_list.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/task_runner.h"
+#include "base/time/time.h"
+#include "content/public/browser/navigation_throttle.h"
+
+// This feature controls whether the DelayNavigationThrottle should be
+// instantiated.
+extern const base::Feature kDelayNavigationFeature;
+
+// DelayNavigationThrottle introduces a delay to main frame navigations.
+class DelayNavigationThrottle : public content::NavigationThrottle {
+ public:
+  // The duration of the delay to add to the start of each navigation, in
+  // milliseconds.
+  static const char kParamDelayNavigationDurationMillis[];
+
+  // The probability that the navigation delay should be introduced. Should be a
+  // double in the interval [0, 1], where a value of 0 indicates the delay
+  // should never be introduced, and a value of 1 indicates the delay should
+  // always be introduced.
+  static const char kParamDelayNavigationProbability[];
+
+  // Creates a DelayNavigationThrottle if the DelayNavigation feature is
+  // enabled and configured.
+  static std::unique_ptr<content::NavigationThrottle> MaybeCreateThrottleFor(
+      content::NavigationHandle* handle);
+
+  // Creates a DelayNavigationThrottle directly. Only intended for use in
+  // tests. Production code should use MaybeCreateThrottleFor.
+  DelayNavigationThrottle(content::NavigationHandle* handle,
+                          scoped_refptr<base::TaskRunner> task_runner,
+                          base::TimeDelta navigation_delay);
+  ~DelayNavigationThrottle() override;
+
+  // content::NavigationThrottle:
+  content::NavigationThrottle::ThrottleCheckResult WillStartRequest() override;
+
+ private:
+  void OnDelayComplete();
+
+  const scoped_refptr<base::TaskRunner> task_runner_;
+  const base::TimeDelta navigation_delay_;
+
+  // This has to be the last member of the class.
+  base::WeakPtrFactory<DelayNavigationThrottle> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(DelayNavigationThrottle);
+};
+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_EXPERIMENTS_DELAY_NAVIGATION_THROTTLE_H_