Implement suspend/resume for IntersectionObserver 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"
 
 namespace blink {
 
 typedef HeapVector<Member<IntersectionObserver>> IntersectionObserverVector;
 
-IntersectionObserverController::IntersectionObserverController()
-    : m_timer(this, &IntersectionObserverController::deliverIntersectionObservations)
+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_timerFiredWhileSuspended(false)
 {
 }
 
 IntersectionObserverController::~IntersectionObserverController() { }
 
 void IntersectionObserverController::scheduleIntersectionObserverForDelivery(IntersectionObserver& observer)
 {
     // TODO(szager): use idle callback with a timeout
     if (!m_timer.isActive())
         m_timer.startOneShot(0, BLINK_FROM_HERE);
     m_pendingIntersectionObservers.add(&observer);
 }
 
+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).
+    if (m_timerFiredWhileSuspended) {
+        m_timerFiredWhileSuspended = false;
+        deliverIntersectionObservations(nullptr);
+    }
+}
+
 void IntersectionObserverController::deliverIntersectionObservations(Timer<IntersectionObserverController>*)
 {
+    if (executionContext()->activeDOMObjectsAreSuspended()) {
+        m_timerFiredWhileSuspended = true;
+        return;
+    }
     IntersectionObserverVector observers;
     copyToVector(m_pendingIntersectionObservers, observers);
     m_pendingIntersectionObservers.clear();
     for (auto& observer : observers)
         observer->deliver();
 }
 
 void IntersectionObserverController::computeTrackedIntersectionObservations()
 {
     // TODO(szager): Need to define timestamp.
     double timestamp = currentTime();
-    for (auto& observer : m_trackedIntersectionObservers)
+    for (auto& observer : m_trackedIntersectionObservers) {
         observer->computeIntersectionObservations(timestamp);
+        if (observer->hasEntries())
+            scheduleIntersectionObserverForDelivery(*observer);
+    }
 }
 
 void IntersectionObserverController::addTrackedObserver(IntersectionObserver& observer)
 {
     m_trackedIntersectionObservers.add(&observer);
 }
 
 void IntersectionObserverController::removeTrackedObserversForRoot(const Element& root)
 {
     HeapVector<Member<IntersectionObserver>> toRemove;
     for (auto& observer : m_trackedIntersectionObservers) {
         if (observer->root() == &root)
             toRemove.append(observer);
     }
     m_trackedIntersectionObservers.removeAll(toRemove);
 }
 
 DEFINE_TRACE(IntersectionObserverController)
 {
+    ActiveDOMObject::trace(visitor);
     visitor->trace(m_trackedIntersectionObservers);
     visitor->trace(m_pendingIntersectionObservers);
 }
 
 } // namespace blink