Call Element::rebuildLayoutTree from Document::updateStyle directly

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 7aae88c83b5a16951b3eb756e306129b334a7f90..8502f9bf89cf5abd7e0719a234ef30557fae738d 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -1857,7 +1857,6 @@ void Element::recalcStyle(StyleRecalcChange change) {
     if (parentComputedStyle())
       change = recalcOwnStyle(change);
     clearNeedsStyleRecalc();
-    clearNeedsReattachLayoutTree();
   }
 
   // If we reattached we don't need to recalc the style of our descendants
@@ -1876,6 +1875,7 @@ void Element::recalcStyle(StyleRecalcChange change) {
           root->recalcStyle(change);
       }
       recalcDescendantStyles(change);
+      clearChildNeedsStyleRecalc();
     }
 
     updatePseudoElement(PseudoIdAfter, change);
@@ -1887,9 +1887,6 @@ void Element::recalcStyle(StyleRecalcChange change) {
     // non-floating we have to take it into account for the first letter.
     updatePseudoElement(PseudoIdFirstLetter,
                         childNeedsStyleRecalc() ? Force : change);
-
-    clearChildNeedsStyleRecalc();
-    clearChildNeedsReattachLayoutTree();
   }
 
   if (hasCustomStyleCallbacks())
@@ -1943,7 +1940,7 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change) {
   if (localChange == Reattach) {
     document().addNonAttachedStyle(*this, std::move(newStyle));
     setNeedsReattachLayoutTree();
-    return rebuildLayoutTree();
+    return Reattach;
   }
 
   DCHECK(oldStyle);
@@ -1985,33 +1982,52 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change) {
   return localChange;
 }
 
-StyleRecalcChange Element::rebuildLayoutTree() {
+void Element::rebuildLayoutTree() {
   DCHECK(inActiveDocument());
+  DCHECK(!needsStyleRecalc());
+  DCHECK(!childNeedsStyleRecalc());
+  DCHECK(parentNode());
+  DCHECK(parentNode()->childNeedsReattachLayoutTree());
+
   AttachContext reattachContext;
   reattachContext.resolvedStyle = document().getNonAttachedStyle(*this);
   bool layoutObjectWillChange = needsAttach() || layoutObject();
 
-  // We are calling Element::rebuildLayoutTree() from inside
-  // Element::recalcOwnStyle where we set the NeedsReattachLayoutTree
-  // flag - so needsReattachLayoutTree() should always be true.
-  DCHECK(parentNode());
-  DCHECK(parentNode()->childNeedsReattachLayoutTree());
-  DCHECK(needsReattachLayoutTree());
-  reattachLayoutTree(reattachContext);
-  // Since needsReattachLayoutTree() is always true we go into
-  // reattachLayoutTree() which reattaches all the descendant
-  // sub-trees. At this point no child should need reattaching.
+  if (needsReattachLayoutTree()) {
+    reattachLayoutTree(reattachContext);
+  } else if (childNeedsReattachLayoutTree()) {

[esprehn, 2016/11/07 22:32:08]

You're missing:

  SelectorFilterParentScope filterScope(*this);
  StyleSharingDepthScope sharingScope(*this);

which is why you're failing asserts.

Also the PseudoIdBefore. :)

+    rebuildShadowRootLayoutTree();
+    rebuildDescendantLayoutTree();
+    reattachPseudoElementLayoutTree(PseudoIdAfter);
+    reattachPseudoElementLayoutTree(PseudoIdBackdrop);
+  }
+  DCHECK(!needsReattachLayoutTree());
   DCHECK(!childNeedsReattachLayoutTree());
 
   if (layoutObjectWillChange || layoutObject()) {
     // nextTextSibling is passed on to recalcStyle from recalcDescendantStyles
     // we can either traverse the current subtree from this node onwards
     // or store it.
-    // The choice is between increased time and increased memory complexity.
+    // The choice is between increased time and increased memory complexity
+    // (for the duration of Style recalc and Layout Tree Construction).
+    // TODO(bugsnash): This is a performance regression - bugsnash is working on
+    // alleviating this regression.
     reattachWhitespaceSiblingsIfNeeded(nextTextSibling());
-    return Reattach;
   }
-  return ReattachNoLayoutObject;

[esprehn, 2016/11/07 22:32:08]

Is ReattachNoLayoutObject dead code now?

+}
+
+void Element::rebuildShadowRootLayoutTree() {
+  for (ShadowRoot* root = youngestShadowRoot(); root;
+       root = root->olderShadowRoot()) {
+    if (root->needsReattachLayoutTree() || root->childNeedsReattachLayoutTree())
+      root->rebuildLayoutTree();
+  }
+}
+void Element::reattachPseudoElementLayoutTree(PseudoId pseudoId) {
+  if (PseudoElement* element = pseudoElement(pseudoId)) {
+    if (element->needsReattachLayoutTree())
+      element->rebuildLayoutTree();
+  }
 }
 
 void Element::updateCallbackSelectors(const ComputedStyle* oldStyle,