IntersectionObserver: use an idle callback to send notifications.

third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp

 // 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 "core/dom/IntersectionObserverController.h"
 
 #include "core/dom/Document.h"
+#include "core/dom/IdleRequestOptions.h"
 
 namespace blink {
 
 typedef HeapVector<Member<IntersectionObserver>> IntersectionObserverVector;
 
 IntersectionObserverController* IntersectionObserverController::create(Document* document)
 {
     IntersectionObserverController* result = new IntersectionObserverController(document);
     result->suspendIfNeeded();
     return result;
 }
 
 IntersectionObserverController::IntersectionObserverController(Document* document)
     : ActiveDOMObject(document)
-    , m_timer(this, &IntersectionObserverController::deliverIntersectionObservations)
+    , m_timerIsScheduled(false)

[Sami, 2016/03/08 17:32:42]

nit: s/timer/callback/ (here and below)?

[szager1, 2016/03/08 18:51:32]

Done.

     , m_timerFiredWhileSuspended(false)
 {
 }
 
 IntersectionObserverController::~IntersectionObserverController() { }
 
 void IntersectionObserverController::scheduleIntersectionObserverForDelivery(IntersectionObserver& observer)
 {
     // TODO(szager): use idle callback with a timeout.  Until we do that, there is no

[Sami, 2016/03/08 17:32:42]

Did you mean to remove this TODO?

[szager1, 2016/03/08 18:51:32]

Done.

     // reliable way to write a test for takeRecords, because it's impossible to guarantee
     // that javascript will get a chance to run before the timer fires.
-    if (!m_timer.isActive())
-        m_timer.startOneShot(0, BLINK_FROM_HERE);
     m_pendingIntersectionObservers.add(&observer);
+    if (m_timerIsScheduled)
+        return;
+    Document* document = toDocument(executionContext());
+    if (!document)
+        return;
+    m_timerIsScheduled = true;
+    IdleRequestOptions options;
+    options.setTimeout(100);

[haraken, 2016/03/08 03:44:03]

We want to remove hard-coded timers in the future though... For example, 100 ms
would have a different meaning on desktops and low-RAM devices.

[szager1, 2016/03/08 18:51:32]

100ms is required by the IntersectionObserver spec.  I suppose we might opt for
a smaller number here under some circumstances, but I think we can cross that
bridge when we come to it.

[haraken, 2016/03/08 23:05:58]

Then maybe worth adding a comment and mention that this is not an arbitrary
selected number.

[szager1, 2016/03/08 23:12:02]

Done.

+    document->requestIdleCallback(this, options);
 }
 
 void IntersectionObserverController::resume()
 {
     // If the timer fired while DOM objects were suspended, notifications might be late, so deliver
-    // them right away (rather than waiting for m_timer to fire again).
+    // them right away (rather than waiting to fire again).
     if (m_timerFiredWhileSuspended) {
         m_timerFiredWhileSuspended = false;
-        deliverIntersectionObservations(nullptr);
+        deliverIntersectionObservations();
     }
 }
 
-void IntersectionObserverController::deliverIntersectionObservations(Timer<IntersectionObserverController>*)
+void IntersectionObserverController::handleEvent(IdleDeadline*)
+{
+    m_timerIsScheduled = false;
+    deliverIntersectionObservations();
+}
+
+void IntersectionObserverController::deliverIntersectionObservations()
 {
     if (executionContext()->activeDOMObjectsAreSuspended()) {
         m_timerFiredWhileSuspended = true;
         return;
     }
     IntersectionObserverVector observers;
     copyToVector(m_pendingIntersectionObservers, observers);
     m_pendingIntersectionObservers.clear();
     for (auto& observer : observers)
         observer->deliver();
@@ skipping 21 matching lines @@
             toRemove.append(observer);
     }
     m_trackedIntersectionObservers.removeAll(toRemove);
 }
 
 DEFINE_TRACE(IntersectionObserverController)
 {
     visitor->trace(m_trackedIntersectionObservers);
     visitor->trace(m_pendingIntersectionObservers);
     ActiveDOMObject::trace(visitor);
+    IdleRequestCallback::trace(visitor);
 }
 
 } // namespace blink