DCHECK not marking style dirty during layout tree rebuild.

And that we do not re-enter RebuildLayoutTree.

Bug: 868810
Change-Id: Icb70557747c26ccd107775919034ec91b054d070
Reviewed-on: https://chromium-review.googlesource.com/1217743Reviewed-by: Anders Ruud <andruud@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590224}

third_party/blink/renderer/core/css/style_engine.cc

@@ -1555,9 +1555,12 @@ void StyleEngine::RecalcStyle(StyleRecalcChange change) {
 void StyleEngine::RebuildLayoutTree() {
   DCHECK(GetDocument().documentElement());
   DCHECK(GetDocument().ChildNeedsReattachLayoutTree());
+  DCHECK(!InRebuildLayoutTree());
+  in_layout_tree_rebuild_ = true;
 
   WhitespaceAttacher whitespace_attacher;
   GetDocument().documentElement()->RebuildLayoutTree(whitespace_attacher);
+  in_layout_tree_rebuild_ = false;
 }
 
 void StyleEngine::Trace(blink::Visitor* visitor) {

third_party/blink/renderer/core/css/style_engine.h

@@ -321,6 +321,7 @@ class CORE_EXPORT StyleEngine final
 
   void RecalcStyle(StyleRecalcChange change);
   void RebuildLayoutTree();
+  bool InRebuildLayoutTree() const { return in_layout_tree_rebuild_; }
 
   void Trace(blink::Visitor*) override;
   const char* NameInHeapSnapshot() const override { return "StyleEngine"; }
@@ -448,6 +449,7 @@ class CORE_EXPORT StyleEngine final
 
   bool uses_rem_units_ = false;
   bool ignore_pending_stylesheets_ = false;
+  bool in_layout_tree_rebuild_ = false;
 
   Member<StyleResolver> resolver_;
   Member<ViewportStyleResolver> viewport_resolver_;

third_party/blink/renderer/core/dom/node.cc

@@ -905,6 +905,7 @@ void Node::SetNeedsReattachLayoutTree() {
 
 void Node::SetNeedsStyleRecalc(StyleChangeType change_type,
                                const StyleChangeReasonForTracing& reason) {
+  DCHECK(!GetDocument().GetStyleEngine().InRebuildLayoutTree());
   DCHECK(change_type != kNoStyleChange);
   if (!InActiveDocument())
     return;