Add DelayNavigationThrottle

chrome/browser/loader/delay_navigation_throttle.cc

Index: chrome/browser/loader/delay_navigation_throttle.cc
diff --git a/chrome/browser/loader/delay_navigation_throttle.cc b/chrome/browser/loader/delay_navigation_throttle.cc
new file mode 100644
index 0000000000000000000000000000000000000000..174c4429d1f638cc70beaa3e33852c7ba6458237
--- /dev/null
+++ b/chrome/browser/loader/delay_navigation_throttle.cc
@@ -0,0 +1,81 @@
+// 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/loader/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/search/search.h"
+#include "content/public/browser/browser_thread.h"

[Charlie Harrison, 2017/03/22 15:30:12]

Is it used?

[Bryan McQuade, 2017/03/22 18:00:01]

nope - removed, thanks!

+#include "content/public/browser/navigation_handle.h"
+
+const base::Feature kDelayNavigationFeature{"DelayNavigation",
+                                            base::FEATURE_DISABLED_BY_DEFAULT};
+
+const char DelayNavigationThrottle::kParamDelayNavigationDurationMillis[] =
+    "delay_millis";
+
+const char DelayNavigationThrottle::kParamDelayNavigationProbability[] =
+    "delay_probability";
+
+// static
+std::unique_ptr<content::NavigationThrottle>
+DelayNavigationThrottle::MaybeCreateThrottleFor(
+    content::NavigationHandle* handle) {
+  // Never delay:
+  // * non HTTP/HTTPS URLs
+  // * the new tab page, which in some cases has an HTTPS URL
+  if (!handle->GetURL().SchemeIsHTTPOrHTTPS() ||
+      search::IsInstantNTP(handle->GetWebContents())) {

[Charlie Harrison, 2017/03/22 15:30:12]

Is this correct? IsInstantNTP looks at the visible navigation entry. Is this the
proper NTP URL before navigation commit?

[Bryan McQuade, 2017/03/22 18:00:01]

interesting, thanks for digging in. it does seem to have the intended behavior,
but given the comment, i probably should not rely on it. instead, i've changed
it to compare on the URL.

+    return nullptr;
+  }
+
+  if (!base::FeatureList::IsEnabled(kDelayNavigationFeature))

[Charlie Harrison, 2017/03/22 15:30:12]

Let's move this to be the first check. IsInstantNTP looks like a pretty
reasonably expensive function, with GURL allocations and multiple map lookups.

[Bryan McQuade, 2017/03/22 18:00:01]

done

+    return nullptr;
+
+  int navigation_delay_millis = base::GetFieldTrialParamByFeatureAsInt(
+      kDelayNavigationFeature, kParamDelayNavigationDurationMillis,
+      -1 /* default value */);
+
+  if (navigation_delay_millis <= 0)
+    return nullptr;
+
+  double delay_probability = base::GetFieldTrialParamByFeatureAsDouble(
+      kDelayNavigationFeature, kParamDelayNavigationProbability,
+      0 /* default value */);
+
+  if (delay_probability == 0 || delay_probability < base::RandDouble())
+    return nullptr;
+
+  return base::WrapUnique(new DelayNavigationThrottle(

[Charlie Harrison, 2017/03/22 15:30:12]

nit: base::MakeUnique is preferred to avoid bare "new".

[Bryan McQuade, 2017/03/22 18:00:01]

done

+      handle, base::ThreadTaskRunnerHandle::Get(),
+      base::TimeDelta::FromMilliseconds(navigation_delay_millis)));
+}
+
+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();
+}