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..e6f752ae7e7240e4602177dabcc0248e9a66800f 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -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
@@ -1893,9 +1894,6 @@ void Element::recalcStyle(StyleRecalcChange change, Text* nextTextSibling) {
 
   if (hasCustomStyleCallbacks())
     didRecalcStyle(change);
-
-  if (change == Reattach)
-    reattachWhitespaceSiblingsIfNeeded(nextTextSibling);

[esprehn, 2016/10/18 02:00:10]

We don't need the nextTextSibling here anymore so we could remove the argument
in a follow up patch?

 }
 
 PassRefPtr<ComputedStyle> Element::propagateInheritedProperties(
@@ -1944,6 +1942,7 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change) {
 
   if (localChange == Reattach) {
     document().addNonAttachedStyle(*this, std::move(newStyle));
+    setNeedsReattachLayoutTree();
     return rebuildLayoutTree();
   }
 
@@ -1987,12 +1986,31 @@ 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;
 }