IntersectionObserver: use an idle callback to send notifications.

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

Index: third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp b/third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp
index 055b3c64c4bf36f518927d131f177cd7b6840ed4..5b71c685889d2d4d00020ff01b8f133dbd7a66c0 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp
@@ -5,6 +5,7 @@
 #include "core/dom/IntersectionObserverController.h"
 
 #include "core/dom/Document.h"
+#include "core/dom/IdleRequestOptions.h"
 
 namespace blink {
 
@@ -19,8 +20,8 @@ IntersectionObserverController* IntersectionObserverController::create(Document*
 
 IntersectionObserverController::IntersectionObserverController(Document* document)
     : ActiveDOMObject(document)
-    , m_timer(this, &IntersectionObserverController::deliverIntersectionObservations)
-    , m_timerFiredWhileSuspended(false)
+    , m_callbackIsScheduled(false)
+    , m_callbackFiredWhileSuspended(false)
 {
 }
 
@@ -28,28 +29,39 @@ IntersectionObserverController::~IntersectionObserverController() { }
 
 void IntersectionObserverController::scheduleIntersectionObserverForDelivery(IntersectionObserver& observer)
 {
-    // TODO(szager): use idle callback with a timeout.  Until we do that, there is no
-    // 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_callbackIsScheduled)
+        return;
+    Document* document = toDocument(getExecutionContext());
+    if (!document)
+        return;
+    m_callbackIsScheduled = true;
+    IdleRequestOptions options;
+    // The IntersectionObserver spec mandates that notifications be sent within 100ms.
+    options.setTimeout(100);
+    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).
-    if (m_timerFiredWhileSuspended) {
-        m_timerFiredWhileSuspended = false;
-        deliverIntersectionObservations(nullptr);
+    // If the callback fired while DOM objects were suspended, notifications might be late, so deliver
+    // them right away (rather than waiting to fire again).
+    if (m_callbackFiredWhileSuspended) {
+        m_callbackFiredWhileSuspended = false;
+        deliverIntersectionObservations();
     }
 }
 
-void IntersectionObserverController::deliverIntersectionObservations(Timer<IntersectionObserverController>*)
+void IntersectionObserverController::handleEvent(IdleDeadline*)
+{
+    m_callbackIsScheduled = false;
+    deliverIntersectionObservations();
+}
+
+void IntersectionObserverController::deliverIntersectionObservations()
 {
     if (getExecutionContext()->activeDOMObjectsAreSuspended()) {
-        m_timerFiredWhileSuspended = true;
+        m_callbackFiredWhileSuspended = true;
         return;
     }
     IntersectionObserverVector observers;
@@ -88,6 +100,7 @@ DEFINE_TRACE(IntersectionObserverController)
     visitor->trace(m_trackedIntersectionObservers);
     visitor->trace(m_pendingIntersectionObservers);
     ActiveDOMObject::trace(visitor);
+    IdleRequestCallback::trace(visitor);
 }
 
 } // namespace blink