Don't ClearDistribution() until we update it.

With FlatTreeStyleRecalc we expect to traverse up the current flat tree
ancestor chain even when the distribution is marked dirty. Otherwise,
we will not be able to reach the style dirty nodes marked when we have
a dirty distribution.

Bug: 1023178
Change-Id: I2b80ad252bc17bb223a3caa9336526c9e2fb6387
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1911208Reviewed-by: Mason Freed <masonfreed@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714855}

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

@@ -527,4 +527,43 @@ TEST_F(NodeTest, UpdateChildDirtyAfterSlottingDirtyNode) {
   EXPECT_TRUE(span->NeedsStyleRecalc());
 }
 
+TEST_F(NodeTest, ChildDirtyNeedsV0Distribution) {
+  ScopedFlatTreeStyleRecalcForTest scope(true);
+
+  SetBodyContent("<div id=host><span></span> </div>");
+  ShadowRoot* shadow_root = CreateShadowRootForElementWithIDAndSetInnerHTML(
+      GetDocument(), "host", "<content />");
+  UpdateAllLifecyclePhasesForTest();
+
+#if DCHECK_IS_ON()
+  GetDocument().SetAllowDirtyShadowV0Traversal(true);
+#endif
+
+  auto* host = GetDocument().getElementById("host");
+  auto* span = To<Element>(host->firstChild());
+  auto* content = shadow_root->firstChild();
+
+  host->lastChild()->remove();
+
+  EXPECT_FALSE(GetDocument().documentElement()->ChildNeedsStyleRecalc());
+  EXPECT_TRUE(GetDocument().documentElement()->ChildNeedsDistributionRecalc());
+  EXPECT_EQ(content, host->firstChild()->GetStyleRecalcParent());
+  EXPECT_FALSE(content->ChildNeedsStyleRecalc());
+
+  // Make the span style dirty.
+  span->setAttribute("style", "color:green");
+
+  // Check that the flat tree ancestor chain is child-dirty while the
+  // shadow distribution is still dirty.
+  EXPECT_TRUE(GetDocument().documentElement()->ChildNeedsStyleRecalc());
+  EXPECT_TRUE(GetDocument().body()->ChildNeedsStyleRecalc());
+  EXPECT_TRUE(host->ChildNeedsStyleRecalc());
+  EXPECT_TRUE(content->ChildNeedsStyleRecalc());
+  EXPECT_TRUE(GetDocument().documentElement()->ChildNeedsDistributionRecalc());
+
+#if DCHECK_IS_ON()
+  GetDocument().SetAllowDirtyShadowV0Traversal(false);
+#endif
+}
+
 }  // namespace blink

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

@@ -248,8 +248,6 @@ void ShadowRoot::SetNeedsDistributionRecalc() {
     return;
   needs_distribution_recalc_ = true;
   host().MarkAncestorsWithChildNeedsDistributionRecalc();
-  if (!IsV1())
-    V0().ClearDistribution();
 }
 
 void ShadowRoot::Trace(Visitor* visitor) {

third_party/blink/renderer/core/dom/shadow_root_v0.cc

@@ -168,6 +168,8 @@ const DestinationInsertionPoints* ShadowRootV0::DestinationInsertionPointsFor(
 }
 
 void ShadowRootV0::Distribute() {
+  ClearDistribution();
+
   DistributionPool pool(GetShadowRoot().host());
   HTMLShadowElement* shadow_insertion_point = nullptr;