Don't use cached ComputedStyle when flat-tree flag differs.

If we cache a ComputedStyle which is computed outside of the flat tree,
any pending resources will stay StylePendingImage. That means we cannot
use such a ComputedStyle for cached styles for a rendered element.

We already did this check for display:none subtree ComputedStyles, but
we need the same check for IsEnsuredOutsideFlatTree().

Bug: 1095669
Change-Id: Ide7395207a6d73b78bc793e4ee4c10cf31b9696f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250201Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779530}

third_party/blink/renderer/core/css/resolver/matched_properties_cache.cc

@@ -92,13 +92,15 @@ bool CachedMatchedProperties::DependenciesEqual(
     const StyleResolverState& state) {
   if (!state.ParentStyle())
     return false;
-  if (parent_computed_style->IsEnsuredInDisplayNone() &&
-      !state.ParentStyle()->IsEnsuredInDisplayNone()) {
-    // If we cached a ComputedStyle in a display:none subtree we would not have
-    // triggered fetches for external resources and have StylePendingImages in
-    // the ComputedStyle. Instead of having to inspect the cached ComputedStyle
-    // for such resources, don't use a cached ComputedStyle when it was cached
-    // in display:none but is now rendered.
+  if ((parent_computed_style->IsEnsuredInDisplayNone() ||
+       computed_style->IsEnsuredOutsideFlatTree()) &&
+      !state.ParentStyle()->IsEnsuredInDisplayNone() &&
+      !state.Style()->IsEnsuredOutsideFlatTree()) {
+    // If we cached a ComputedStyle in a display:none subtree, or outside the
+    // flat tree,  we would not have triggered fetches for external resources
+    // and have StylePendingImages in the ComputedStyle. Instead of having to
+    // inspect the cached ComputedStyle for such resources, don't use a cached
+    // ComputedStyle when it was cached in display:none but is now rendered.
     return false;
   }
 

third_party/blink/renderer/core/css/resolver/matched_properties_cache_test.cc

@@ -547,4 +547,42 @@ TEST_F(MatchedPropertiesCacheTest, EnsuredInDisplayNone) {
   EXPECT_TRUE(cache.Find(key1, *style, *ensured_parent));
 }
 
+TEST_F(MatchedPropertiesCacheTest, EnsuredOutsideFlatTree) {
+  TestCache cache(GetDocument());
+
+  auto style = CreateStyle();
+  auto parent = CreateStyle();
+  auto ensured_style = CreateStyle();
+  ensured_style->SetIsEnsuredOutsideFlatTree();
+
+  TestKey key1("display:block", 1);
+
+  cache.Add(key1, *style, *parent);
+  EXPECT_TRUE(cache.Find(key1, *style, *parent));
+  EXPECT_TRUE(cache.Find(key1, *ensured_style, *parent));
+
+  cache.Add(key1, *ensured_style, *parent);
+  EXPECT_FALSE(cache.Find(key1, *style, *parent));
+  EXPECT_TRUE(cache.Find(key1, *ensured_style, *parent));
+}
+
+TEST_F(MatchedPropertiesCacheTest, EnsuredOutsideFlatTreeAndDisplayNone) {
+  TestCache cache(GetDocument());
+
+  auto parent = CreateStyle();
+  auto parent_none = CreateStyle();
+  auto style = CreateStyle();
+  auto style_flat = CreateStyle();
+  parent_none->SetIsEnsuredInDisplayNone();
+  style_flat->SetIsEnsuredOutsideFlatTree();
+
+  TestKey key1("display:block", 1);
+
+  cache.Add(key1, *style, *parent_none);
+  EXPECT_TRUE(cache.Find(key1, *style_flat, *parent));
+
+  cache.Add(key1, *style_flat, *parent);
+  EXPECT_TRUE(cache.Find(key1, *style, *parent_none));
+}
+
 }  // namespace blink