Create NetworkQuietDetector.

third_party/WebKit/Source/core/loader/NetworkQuietDetector.cpp

+// 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 "core/loader/NetworkQuietDetector.h"
+
+#include "core/dom/TaskRunnerHelper.h"
+#include "core/frame/LocalFrame.h"
+#include "platform/instrumentation/resource_coordinator/FrameResourceCoordinator.h"
+#include "platform/loader/fetch/ResourceFetcher.h"
+
+namespace blink {
+
+static const char kSupplementName[] = "NetworkQuietDetector";
+
+NetworkQuietDetector& NetworkQuietDetector::From(Document& document) {
+  NetworkQuietDetector* detector = static_cast<NetworkQuietDetector*>(
+      Supplement<Document>::From(document, kSupplementName));
+  if (!detector) {
+    detector = new NetworkQuietDetector(document);
+    Supplement<Document>::ProvideTo(document, kSupplementName, detector);
+  }
+  return *detector;
+}
+
+// This function is called when the number of active connections is decreased.

[Zhen Wang, 2017/06/08 16:25:56]

nit: This comment could be misleading that active connections decrease
monotonically.

[lpy, 2017/06/12 18:06:29]

Done.

+void NetworkQuietDetector::CheckNetworkStable() {
+  // Document finishes parsing after DomContentLoadedEventEnd is fired,
+  // check the status in order to avoid false signals.
+  if (!GetDocument()->HasFinishedParsing())
+    return;
+
+  SetNetworkQuietTimers(ActiveConnections());
+}
+
+NetworkQuietDetector::NetworkQuietDetector(Document& document)
+    : Supplement<Document>(document),
+      network2_quiet_timer_(

[Nate Chapin, 2017/06/12 17:16:39]

What's the significance of '2' in this variable name?

[lpy, 2017/06/12 18:06:29]

It means it has no more than 2 active connection. We put a comment in the header
file.

[Nate Chapin, 2017/06/12 18:12:17]

I'd be inclined to leave the number out of the variable name for two reasons:
1. If you change the number of connections, you can just change a constant
rather than having to rename the variable.
2. I kept reading it as "network too quiet timer", which was confusing. English
is annoying sometimes :(

[dcheng, 2017/06/14 00:12:52]

(I'd echo this comment, except for basically everywhere "2" is used. It's
difficult to tell if it refers to two connections, two seconds, or "to". Might
be easiest to just drop '2' from the variable names given the ambiguity; it's
easy enough to make it clear that this class watches for fewer than 2
connections in comments)

+          TaskRunnerHelper::Get(TaskType::kUnspecedTimer, &document),
+          this,
+          &NetworkQuietDetector::Network2QuietTimerFired) {}
+
+Document* NetworkQuietDetector::GetDocument() {

[Nate Chapin, 2017/06/12 17:16:39]

I don't feel strongly, but it's not clear to me that this helper makes the code
more readable.

[lpy, 2017/06/12 18:06:29]

Done.
I don't think we need it for now, so removed it and replaced with
GetSupplementable().

+  return GetSupplementable();
+}
+
+int NetworkQuietDetector::ActiveConnections() {
+  ResourceFetcher* fetcher = GetDocument()->Fetcher();
+  return fetcher->BlockingRequestCount() + fetcher->NonblockingRequestCount();
+}
+
+void NetworkQuietDetector::SetNetworkQuietTimers(int active_connections) {

[Nate Chapin, 2017/06/12 17:16:39]

This is only called once. Maybe inline it in CheckNetworkStable?

[lpy, 2017/06/12 18:06:29]

We need it in tests.

+  if (network2_quiet_reached_ || active_connections > 2)
+    return;
+
+  // If activeConnections < 2 and the timer is already running, current
+  // 2-quiet window continues; the timer shouldn't be restarted.
+  if (active_connections == 2 || !network2_quiet_timer_.IsActive()) {
+    network2_quiet_timer_.StartOneShot(kNetwork2QuietWindowSeconds,
+                                       BLINK_FROM_HERE);
+  }
+}
+
+void NetworkQuietDetector::Network2QuietTimerFired(TimerBase*) {
+  if (!GetDocument() || !GetDocument()->GetFrame() || network2_quiet_reached_ ||
+      ActiveConnections() > 2)
+    return;
+  network2_quiet_reached_ = true;
+  auto frame_resource_coordinator =
+      GetDocument()->GetFrame()->GetFrameResourceCoordinator();
+  if (frame_resource_coordinator) {
+    frame_resource_coordinator->SendEvent(
+        resource_coordinator::mojom::EventType::kOnLocalFrameNetworkIdle);
+  }
+}
+
+DEFINE_TRACE(NetworkQuietDetector) {
+  Supplement<Document>::Trace(visitor);
+}
+
+}  // namespace blink