IntersectionObserver: use post task inside of resume().

Rather than running callbacks immediately, post a task to run the
callbacks, to avoid conflicts while undeferring a page.

R=dcheng@chromium.org
BUG=670092

Review-Url: https://codereview.chromium.org/2565863002
Cr-Commit-Position: refs/heads/master@{#438043}

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

@@ -26,9 +26,7 @@ IntersectionObserverController::IntersectionObserverController(
 
 IntersectionObserverController::~IntersectionObserverController() {}
 
-void IntersectionObserverController::scheduleIntersectionObserverForDelivery(
-    IntersectionObserver& observer) {
-  m_pendingIntersectionObservers.add(&observer);
+void IntersectionObserverController::postTaskToDeliverObservations() {
   if (!m_weakPtrFactory.hasWeakPtrs()) {
     // TODO(ojan): These tasks decide whether to throttle a subframe, so they
     // need to be unthrottled, but we should throttle all the other tasks
@@ -41,12 +39,18 @@ void IntersectionObserverController::scheduleIntersectionObserverForDelivery(
   }
 }
 
+void IntersectionObserverController::scheduleIntersectionObserverForDelivery(
+    IntersectionObserver& observer) {
+  m_pendingIntersectionObservers.add(&observer);
+  postTaskToDeliverObservations();
+}
+
 void IntersectionObserverController::resume() {
   // 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();
+    postTaskToDeliverObservations();
   }
 }
 

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

@@ -39,6 +39,7 @@ class IntersectionObserverController
 
  private:
   explicit IntersectionObserverController(Document*);
+  void postTaskToDeliverObservations();
 
  private:
   // IntersectionObservers for which this is the tracking document.

third_party/WebKit/Source/web/tests/IntersectionObserverTest.cpp

@@ -6,6 +6,7 @@
 
 #include "core/dom/IntersectionObserverCallback.h"
 #include "core/dom/IntersectionObserverInit.h"
+#include "core/frame/FrameView.h"
 #include "platform/testing/UnitTestHelpers.h"
 #include "web/WebViewImpl.h"
 #include "web/tests/sim/SimCompositor.h"
@@ -67,4 +68,63 @@ TEST_F(IntersectionObserverTest, ObserveSchedulesFrame) {
   EXPECT_TRUE(compositor().needsBeginFrame());
 }
 
+TEST_F(IntersectionObserverTest, ResumePostsTask) {
+  webView().resize(WebSize(800, 600));
+  SimRequest mainResource("https://example.com/", "text/html");
+  loadURL("https://example.com/");
+  mainResource.complete(
+      "<div id='leading-space' style='height: 700px;'></div>"
+      "<div id='target'></div>"
+      "<div id='trailing-space' style='height: 700px;'></div>");
+
+  IntersectionObserverInit observerInit;
+  DummyExceptionStateForTesting exceptionState;
+  TestIntersectionObserverCallback* observerCallback =
+      new TestIntersectionObserverCallback(document());
+  IntersectionObserver* observer = IntersectionObserver::create(
+      observerInit, *observerCallback, exceptionState);
+  ASSERT_FALSE(exceptionState.hadException());
+
+  Element* target = document().getElementById("target");
+  ASSERT_TRUE(target);
+  observer->observe(target, exceptionState);
+
+  compositor().beginFrame();
+  testing::runPendingTasks();
+  EXPECT_EQ(observerCallback->callCount(), 0);
+
+  // When document is not suspended, beginFrame() will generate notifications
+  // and post a task to deliver them.
+  document().view()->layoutViewportScrollableArea()->setScrollOffset(
+      ScrollOffset(0, 300), ProgrammaticScroll);
+  compositor().beginFrame();
+  EXPECT_EQ(observerCallback->callCount(), 0);
+  testing::runPendingTasks();
+  EXPECT_EQ(observerCallback->callCount(), 1);
+
+  // When a document is suspended, beginFrame() will generate a notification,
+  // but it will not be delivered.  The notification will, however, be
+  // available via takeRecords();
+  document().suspendScheduledTasks();
+  document().view()->layoutViewportScrollableArea()->setScrollOffset(
+      ScrollOffset(0, 0), ProgrammaticScroll);
+  compositor().beginFrame();
+  EXPECT_EQ(observerCallback->callCount(), 1);
+  testing::runPendingTasks();
+  EXPECT_EQ(observerCallback->callCount(), 1);
+  EXPECT_FALSE(observer->takeRecords(exceptionState).isEmpty());
+
+  // Generate a notification while document is suspended; then resume document.
+  // Notification should happen in a post task.
+  document().view()->layoutViewportScrollableArea()->setScrollOffset(
+      ScrollOffset(0, 300), ProgrammaticScroll);
+  compositor().beginFrame();
+  testing::runPendingTasks();
+  EXPECT_EQ(observerCallback->callCount(), 1);
+  document().resumeScheduledTasks();
+  EXPECT_EQ(observerCallback->callCount(), 1);
+  testing::runPendingTasks();
+  EXPECT_EQ(observerCallback->callCount(), 2);
+}
+
 }  // namespace blink