Add DelayNavigationThrottle

chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.cc

+// 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.
+
+#include "chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.h"
+
+#include "base/memory/ptr_util.h"
+#include "base/metrics/field_trial_params.h"
+#include "base/rand_util.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/search/search.h"
+#include "content/public/browser/navigation_handle.h"
+#include "content/public/browser/web_contents.h"
+
+namespace {
+
+base::TimeDelta GetNavigationDelayFromParams() {
+  double delay_probability = base::GetFieldTrialParamByFeatureAsDouble(
+      kDelayNavigationFeature,
+      DelayNavigationThrottle::kParamDelayNavigationProbability,
+      0 /* default value */);
+
+  if (delay_probability == 0 || delay_probability < base::RandDouble())

[Charlie Harrison, 2017/03/24 17:06:58]

Can we DCHECK that delay_probability is <= 1?

[Bryan McQuade, 2017/03/24 17:13:57]

sure, good idea. done, thanks!

+    return base::TimeDelta();
+
+  int navigation_delay_millis = base::GetFieldTrialParamByFeatureAsInt(
+      kDelayNavigationFeature,
+      DelayNavigationThrottle::kParamDelayNavigationDurationMillis,
+      -1 /* default value */);
+
+  if (navigation_delay_millis <= 0)
+    return base::TimeDelta();
+
+  bool randomize_delay = base::GetFieldTrialParamByFeatureAsBool(
+      kDelayNavigationFeature,
+      DelayNavigationThrottle::kParamDelayNavigationRandomize,
+      false /* default value */);
+
+  if (randomize_delay) {
+    // RandGenerator produces a value in [0, navigation_delay_millis). We want
+    // a value in [1, navigation_delay_millis].
+    navigation_delay_millis = base::RandGenerator(navigation_delay_millis) + 1;
+  }
+
+  return base::TimeDelta::FromMilliseconds(navigation_delay_millis);
+}
+
+}  // namespace
+
+const base::Feature kDelayNavigationFeature{"DelayNavigation",
+                                            base::FEATURE_DISABLED_BY_DEFAULT};
+
+const char DelayNavigationThrottle::kParamDelayNavigationDurationMillis[] =
+    "delay_millis";
+
+const char DelayNavigationThrottle::kParamDelayNavigationRandomize[] =
+    "randomize_delay";
+
+const char DelayNavigationThrottle::kParamDelayNavigationProbability[] =
+    "delay_probability";
+
+// static
+std::unique_ptr<DelayNavigationThrottle>
+DelayNavigationThrottle::MaybeCreateThrottleFor(
+    content::NavigationHandle* handle) {
+  if (!handle->IsInMainFrame() ||
+      !base::FeatureList::IsEnabled(kDelayNavigationFeature) ||
+      !handle->GetURL().SchemeIsHTTPOrHTTPS()) {
+    return nullptr;
+  }
+
+  // Do not delay the NTP, which in some cases has an HTTPS URL.
+  if (search::IsNTPURL(handle->GetURL(),
+                       Profile::FromBrowserContext(
+                           handle->GetWebContents()->GetBrowserContext()))) {
+    return nullptr;
+  }
+
+  base::TimeDelta navigation_delay = GetNavigationDelayFromParams();
+  if (navigation_delay.is_zero())
+    return nullptr;
+
+  return base::MakeUnique<DelayNavigationThrottle>(
+      handle, base::ThreadTaskRunnerHandle::Get(), navigation_delay);
+}
+
+DelayNavigationThrottle::DelayNavigationThrottle(
+    content::NavigationHandle* handle,
+    scoped_refptr<base::TaskRunner> task_runner,
+    base::TimeDelta navigation_delay)
+    : content::NavigationThrottle(handle),
+      task_runner_(task_runner),
+      navigation_delay_(navigation_delay),
+      weak_ptr_factory_(this) {}
+
+DelayNavigationThrottle::~DelayNavigationThrottle() {}
+
+content::NavigationThrottle::ThrottleCheckResult
+DelayNavigationThrottle::WillStartRequest() {
+  task_runner_->PostDelayedTask(
+      FROM_HERE,
+      base::Bind(&DelayNavigationThrottle::OnDelayComplete,
+                 weak_ptr_factory_.GetWeakPtr()),
+      navigation_delay_);
+  return content::NavigationThrottle::DEFER;
+}
+
+void DelayNavigationThrottle::OnDelayComplete() {
+  navigation_handle()->Resume();
+}