ScheduleLayoutTreeUpdate for dirty slot assignments.

We did not schedule a visual update for dirty slot assignments. If
adding a host child is the only thing that happened for a frame, we
would not run the lifecycle update.

Bug: 1137711
Change-Id: Icd3fe88999129e56c7c6eaa5174f4a89ac4df6c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485099Reviewed-by: Mason Freed <masonfreed@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818804}

third_party/blink/renderer/core/dom/slot_assignment.cc

@@ -232,6 +232,7 @@ void SlotAssignment::SetNeedsAssignmentRecalc() {
   if (owner_->isConnected()) {
     owner_->GetDocument().GetSlotAssignmentEngine().AddShadowRootNeedingRecalc(
         *owner_);
+    owner_->GetDocument().ScheduleLayoutTreeUpdateIfNeeded();
   }
 }
 

third_party/blink/renderer/core/dom/slot_assignment_test.cc

@@ -11,8 +11,9 @@
 #include "third_party/blink/renderer/core/dom/node_traversal.h"
 #include "third_party/blink/renderer/core/dom/shadow_root.h"
 #include "third_party/blink/renderer/core/dom/text.h"
+#include "third_party/blink/renderer/core/frame/local_frame_view.h"
 #include "third_party/blink/renderer/core/html/html_collection.h"
-#include "third_party/blink/renderer/core/html/html_element.h"
+#include "third_party/blink/renderer/core/html/html_div_element.h"
 #include "third_party/blink/renderer/core/html/html_slot_element.h"
 #include "third_party/blink/renderer/core/testing/dummy_page_holder.h"
 #include "third_party/blink/renderer/platform/testing/runtime_enabled_features_test_helpers.h"
@@ -164,4 +165,23 @@ TEST_F(SlotAssignmentTest, AssignedNodesAreSet) {
   EXPECT_EQ(expected_nodes, slot->AssignedNodes());
 }
 
+TEST_F(SlotAssignmentTest, ScheduleVisualUpdate) {
+  SetBody(R"HTML(
+    <div id="host">
+      <shadowroot>
+        <slot></slot>
+      </shadowroot>
+      <div></div>
+    </div>
+  )HTML");
+
+  GetDocument().View()->UpdateAllLifecyclePhases(DocumentUpdateReason::kTest);
+  GetDocument().View()->RunPostLifecycleSteps();
+
+  auto* div = MakeGarbageCollected<HTMLDivElement>(GetDocument());
+  GetDocument().getElementById("host")->appendChild(div);
+  EXPECT_EQ(DocumentLifecycle::kVisualUpdatePending,
+            GetDocument().Lifecycle().GetState());
+}
+
 }  // namespace blink