IO: Don't process post-layout delivery observers in post lifecycle.

This patch extends the previous early out to ensure that we skip
doing work for post-layout observers in post-lifecycle. Previously
the early out only skipped non-post-layout observers in post-layout.

R=szager@chromium.org, chrishtr@chromium.org

Bug: 1165803
Change-Id: I639354ef603fc1aa25598816f6ef2bb8852f1fe3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625128Reviewed-by: Stefan Zager <szager@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842664}

third_party/blink/renderer/core/intersection_observer/intersection_observation.cc

@@ -105,13 +105,15 @@ bool IntersectionObservation::ShouldCompute(unsigned flags) {
     return false;
 
   // If we're processing post-layout deliveries only and we don't have a
-  // post-layout delivery observer, then return early.
-  if (flags & kPostLayoutDeliveryOnly) {
-    if (Observer()->GetDeliveryBehavior() !=
-        IntersectionObserver::kDeliverDuringPostLayoutSteps) {
-      return false;
-    }
-  }
+  // post-layout delivery observer, then return early. Likewise, return if we
+  // need to compute non-post-layout-delivery observations but the observer
+  // behavior is post-layout.
+  bool post_layout_delivery_only = flags & kPostLayoutDeliveryOnly;
+  bool is_post_layout_delivery_observer =
+      Observer()->GetDeliveryBehavior() ==
+      IntersectionObserver::kDeliverDuringPostLayoutSteps;
+  if (post_layout_delivery_only != is_post_layout_delivery_observer)
+    return false;
 
   if (flags &
       (observer_->RootIsImplicit() ? kImplicitRootObserversNeedUpdate

third_party/blink/renderer/core/intersection_observer/intersection_observer.cc

@@ -445,11 +445,16 @@ bool IntersectionObserver::ComputeIntersections(unsigned flags) {
     return false;
 
   // If we're processing post-layout deliveries only and we're not a post-layout
-  // delivery observer, then return early.
-  if (flags & IntersectionObservation::kPostLayoutDeliveryOnly) {
-    if (GetDeliveryBehavior() != kDeliverDuringPostLayoutSteps)
-      return false;
-  }
+  // delivery observer, then return early. Likewise, return if we need to
+  // compute non-post-layout-delivery observations but the observer behavior is
+  // post-layout.
+  bool post_layout_delivery_only =
+      flags & IntersectionObservation::kPostLayoutDeliveryOnly;
+  bool is_post_layout_delivery_observer =
+      GetDeliveryBehavior() ==
+      IntersectionObserver::kDeliverDuringPostLayoutSteps;
+  if (post_layout_delivery_only != is_post_layout_delivery_observer)
+    return false;
 
   IntersectionGeometry::RootGeometry root_geometry(
       IntersectionGeometry::GetRootLayoutObjectForTarget(root(), nullptr,