Move Layout Tree Construction code into Element::rebuildLayoutTree()

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 7a6688b1a524f0d35371390cd52e2ea488d15955..4ccf579e028cb164d8c6d02b63b7a1736dfc647d 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -1835,7 +1835,7 @@ PassRefPtr<ComputedStyle> Element::originalStyleForLayoutObject() {
   return document().ensureStyleResolver().styleForElement(this);
 }
 
-void Element::recalcStyle(StyleRecalcChange change, Text* nextTextSibling) {
+void Element::recalcStyle(StyleRecalcChange change) {
   DCHECK(document().inStyleRecalc());
   DCHECK(!document().lifecycle().inDetach());
   DCHECK(!parentOrShadowHostNode()->needsStyleRecalc());
@@ -1858,6 +1858,7 @@ void Element::recalcStyle(StyleRecalcChange change, Text* nextTextSibling) {
     if (parentComputedStyle())
       change = recalcOwnStyle(change);
     clearNeedsStyleRecalc();
+    clearNeedsReattachLayoutTree();
   }
 
   // If we reattached we don't need to recalc the style of our descendants
@@ -1889,13 +1890,11 @@ void Element::recalcStyle(StyleRecalcChange change, Text* nextTextSibling) {
                         childNeedsStyleRecalc() ? Force : change);
 
     clearChildNeedsStyleRecalc();
+    clearChildNeedsReattachLayoutTree();
   }
 
   if (hasCustomStyleCallbacks())
     didRecalcStyle(change);
-
-  if (change == Reattach)
-    reattachWhitespaceSiblingsIfNeeded(nextTextSibling);
 }
 
 PassRefPtr<ComputedStyle> Element::propagateInheritedProperties(
@@ -1944,6 +1943,7 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change) {
 
   if (localChange == Reattach) {
     document().addNonAttachedStyle(*this, std::move(newStyle));
+    setNeedsReattachLayoutTree();
     return rebuildLayoutTree();
   }
 
@@ -1987,12 +1987,31 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change) {
 }
 
 StyleRecalcChange Element::rebuildLayoutTree() {
+  DCHECK(inActiveDocument());
   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);
-  if (layoutObjectWillChange || layoutObject())
+  // Since needsReattachLayoutTree() is always true we go into
+  // reattachLayoutTree() which reattaches all the descendant
+  // sub-trees. At this point no child should need reattaching.
+  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.
+    reattachWhitespaceSiblingsIfNeeded(nextTextSibling());
     return Reattach;
+  }
   return ReattachNoLayoutObject;
 }