Force an intersection observation after calling observe().

Bug: 742413
Change-Id: I43129261e2c69d32b4e2b31a66d6d4f3bef52a36
Reviewed-on: https://chromium-review.googlesource.com/571417Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487579}

third_party/WebKit/Source/core/frame/LocalFrameView.cpp

@@ -215,6 +215,7 @@ LocalFrameView::LocalFrameView(LocalFrame& frame, IntRect frame_rect)
       suppress_adjust_view_size_(false),
       allows_layout_invalidation_after_layout_clean_(true),
       forcing_layout_parent_view_(false),
+      needs_intersection_observation_(false),
       main_thread_scrolling_reasons_(0) {
   Init();
 }
@@ -4965,6 +4966,7 @@ void LocalFrameView::UpdateViewportIntersectionsForSubtree(
        child = child->Tree().NextSibling()) {
     child->View()->UpdateViewportIntersectionsForSubtree(target_state);
   }
+  needs_intersection_observation_ = false;
 }
 
 void LocalFrameView::UpdateRenderThrottlingStatusForTesting() {
@@ -5125,9 +5127,15 @@ void LocalFrameView::RecordDeferredLoadingStats() {
                                    total_screens_away));
 }
 
+void LocalFrameView::SetNeedsIntersectionObservation() {
+  needs_intersection_observation_ = true;
+  if (LocalFrameView* parent = ParentFrameView())
+    parent->SetNeedsIntersectionObservation();
+}
+
 bool LocalFrameView::ShouldThrottleRendering() const {
-  return CanThrottleRendering() && frame_->GetDocument() &&
-         Lifecycle().ThrottlingAllowed();
+  return CanThrottleRendering() && !needs_intersection_observation_ &&
+         frame_->GetDocument() && Lifecycle().ThrottlingAllowed();
 }
 
 bool LocalFrameView::CanThrottleRendering() const {

third_party/WebKit/Source/core/frame/LocalFrameView.h

@@ -182,6 +182,10 @@ class CORE_EXPORT LocalFrameView final
   void SetNeedsUpdateGeometries() { needs_update_geometries_ = true; }
   void UpdateGeometry() override;
 
+  // Marks this frame, and ancestor frames, as needing one intersection
+  // observervation. This overrides throttling for one frame.
+  void SetNeedsIntersectionObservation();
+
   // Methods for getting/setting the size Blink should use to layout the
   // contents.
   // NOTE: Scrollbar exclusion is based on the LocalFrameView's scrollbars. To
@@ -1191,6 +1195,7 @@ class CORE_EXPORT LocalFrameView final
   bool suppress_adjust_view_size_;
   bool allows_layout_invalidation_after_layout_clean_;
   bool forcing_layout_parent_view_;
+  bool needs_intersection_observation_;
 
   Member<ElementVisibilityObserver> visibility_observer_;
 

third_party/WebKit/Source/core/intersection_observer/IntersectionObserver.cpp

@@ -246,8 +246,12 @@ void IntersectionObserver::observe(Element* target,
       new IntersectionObservation(*this, *target);
   target->EnsureIntersectionObserverData().AddObservation(*observation);
   observations_.insert(observation);
-  if (LocalFrameView* frame_view = target_frame->View())
+  if (LocalFrameView* frame_view = target_frame->View()) {
+    // The IntersectionObsever spec requires that at least one observation
+    // be recorded afer observe() is called, even if the frame is throttled.
+    frame_view->SetNeedsIntersectionObservation();
     frame_view->ScheduleAnimation();
+  }
 }
 
 void IntersectionObserver::unobserve(Element* target,

third_party/WebKit/Source/core/scheduler/FrameThrottlingTest.cpp

@@ -189,6 +189,43 @@ TEST_P(FrameThrottlingTest, HiddenCrossOriginFramesAreThrottled) {
   EXPECT_TRUE(inner_frame_document->View()->CanThrottleRendering());
 }
 
+TEST_P(FrameThrottlingTest, IntersectionObservationOverridesThrottling) {
+  // Create a document with doubly nested iframes.
+  SimRequest main_resource("https://example.com/", "text/html");
+  SimRequest frame_resource("https://example.com/iframe.html", "text/html");
+
+  LoadURL("https://example.com/");
+  main_resource.Complete("<iframe id=frame src=iframe.html></iframe>");
+  frame_resource.Complete("<iframe id=innerFrame sandbox></iframe>");
+
+  auto* frame_element =
+      toHTMLIFrameElement(GetDocument().getElementById("frame"));
+  auto* frame_document = frame_element->contentDocument();
+
+  auto* inner_frame_element =
+      toHTMLIFrameElement(frame_document->getElementById("innerFrame"));
+  auto* inner_frame_document = inner_frame_element->contentDocument();
+
+  DocumentLifecycle::AllowThrottlingScope throttling_scope(
+      GetDocument().Lifecycle());
+
+  // Hidden cross origin frames are throttled.
+  frame_element->setAttribute(styleAttr, "transform: translateY(480px)");
+  CompositeFrame();
+  EXPECT_FALSE(GetDocument().View()->CanThrottleRendering());
+  EXPECT_FALSE(frame_document->View()->CanThrottleRendering());
+  EXPECT_TRUE(inner_frame_document->View()->ShouldThrottleRendering());
+
+  // An intersection observation overrides...
+  inner_frame_document->View()->SetNeedsIntersectionObservation();
+  EXPECT_FALSE(inner_frame_document->View()->ShouldThrottleRendering());
+  inner_frame_document->View()->ScheduleAnimation();
+
+  CompositeFrame();
+  // ...but only for one frame.
+  EXPECT_TRUE(inner_frame_document->View()->ShouldThrottleRendering());
+}
+
 TEST_P(FrameThrottlingTest, HiddenCrossOriginZeroByZeroFramesAreNotThrottled) {
   // Create a document with doubly nested iframes.
   SimRequest main_resource("https://example.com/", "text/html");