Support display: contents for elements, first-line and first-letter pseudos.

third_party/WebKit/Source/core/dom/Element.cpp

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index 469bc7a952c742e9449d340a4b81df0a039a8166..a5d4867ec8678c508135c87fc9a69df3ed48df64 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -1529,7 +1529,8 @@ const AtomicString Element::imageSourceURL() const {
 }
 
 bool Element::layoutObjectIsNeeded(const ComputedStyle& style) {
-  return style.display() != EDisplay::None;
+  return style.display() != EDisplay::None &&
+         style.display() != EDisplay::Contents;
 }
 
 LayoutObject* Element::createLayoutObject(const ComputedStyle& style) {
@@ -1667,9 +1668,15 @@ void Element::attachLayoutTree(const AttachContext& context) {
     data->clearComputedStyle();
   }
 
-  if (!isActiveSlotOrActiveInsertionPoint())
-    LayoutTreeBuilderForElement(*this, context.resolvedStyle)
-        .createLayoutObjectIfNeeded();
+  if (!isActiveSlotOrActiveInsertionPoint()) {
+    LayoutTreeBuilderForElement builder(*this, context.resolvedStyle);
+    builder.createLayoutObjectIfNeeded();
+
+    if (ComputedStyle* style = builder.resolvedStyle()) {
+      if (!layoutObject() && shouldStoreNonLayoutObjectComputedStyle(*style))
+        storeNonLayoutObjectComputedStyle(style);
+    }
+  }
 
   addCallbackSelectors();
 
@@ -1692,6 +1699,22 @@ void Element::attachLayoutTree(const AttachContext& context) {
 
   ContainerNode::attachLayoutTree(context);
 
+  // Quite unfortunately, if we're a display: contents node reattaching our
+  // subtree we need to reattach the parent's *after* attaching all our
+  // children. We might be able to be more granular here, but otherwise we don't
+  // always properly rebuild the layout tree due to anonymous boxes, for
+  // example. See css-display-3/display-contents-reattachment.html, which fails
+  // without this, for example, due to misplaced flex anonymous blocks.
+  //
+  // Also, don't do it if we're a pseudo-element, because it's pointless and
+  // causes infinite recursion if the parent doesn't have display: contents.
+  if (hasDisplayContentsStyle() && !isPseudoElement() && parentNode() &&
+      !parentNode()->needsAttach()) {
+    parentNode()->reattachLayoutTree();
+    DCHECK(!needsAttach());
+    return;
+  }
+
   createPseudoElementIfNeeded(PseudoIdAfter);
   createPseudoElementIfNeeded(PseudoIdBackdrop);
 
@@ -1966,6 +1989,9 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change) {
       // https://codereview.chromium.org/30453002/
       layoutObject->setStyleInternal(newStyle.get());
     }
+  } else if (localChange != NoChange &&
+             shouldStoreNonLayoutObjectComputedStyle(*newStyle)) {
+    storeNonLayoutObjectComputedStyle(newStyle);
   }
 
   if (getStyleChangeType() >= SubtreeStyleChange)
@@ -3128,6 +3154,42 @@ const ComputedStyle* Element::ensureComputedStyle(
   return elementStyle->addCachedPseudoStyle(result.release());
 }
 
+const ComputedStyle* Element::nonLayoutObjectComputedStyle() const {
+  if (layoutObject() || !hasRareData())
+    return nullptr;
+
+  return elementRareData()->computedStyle();
+}
+
+bool Element::hasDisplayContentsStyle() const {
+  if (const ComputedStyle* style = nonLayoutObjectComputedStyle())
+    return style->display() == EDisplay::Contents;
+  return false;
+}
+
+bool Element::shouldStoreNonLayoutObjectComputedStyle(
+    const ComputedStyle& style) const {
+#if DCHECK_IS_ON()
+  if (style.display() == EDisplay::Contents)
+    DCHECK(!layoutObject());
+#endif
+
+  return style.display() == EDisplay::Contents ||
+         isHTMLOptGroupElement(*this) || isHTMLOptionElement(*this);
+}
+
+void Element::storeNonLayoutObjectComputedStyle(
+    PassRefPtr<ComputedStyle> style) {
+  DCHECK(style);
+  DCHECK(shouldStoreNonLayoutObjectComputedStyle(*style));
+  ensureElementRareData().setComputedStyle(std::move(style));
+}
+
+void Element::clearNonLayoutObjectComputedStyle() {
+  DCHECK(nonLayoutObjectComputedStyle());
+  elementRareData()->clearComputedStyle();
+}
+
 AtomicString Element::computeInheritedLanguage() const {
   const Node* n = this;
   AtomicString value;
@@ -3863,6 +3925,7 @@ void Element::inlineStyleChanged() {
                                             StyleChangeReason::Inline));
   DCHECK(elementData());
   elementData()->m_styleAttributeIsDirty = true;
+
   InspectorInstrumentation::didInvalidateStyleAttr(this);
 
   if (MutationObserverInterestGroup* recipients =