Call Element::rebuildLayoutTree from Document::updateStyle directly

third_party/WebKit/Source/core/dom/shadow/ShadowRoot.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 129 matching lines @@
   // ShadowRoot doesn't support custom callbacks.
   DCHECK(!hasCustomStyleCallbacks());
 
   StyleSharingDepthScope sharingScope(*this);
 
   if (getStyleChangeType() >= SubtreeStyleChange)
     change = Force;
 
   // There's no style to update so just calling recalcStyle means we're updated.
   clearNeedsStyleRecalc();
-  clearNeedsReattachLayoutTree();
 
   recalcDescendantStyles(change);
   clearChildNeedsStyleRecalc();
+  // Currently only the NeedsReattachLayoutTree flag is set on the ShadowRoot.
+  // Need to tell the ancestor nodes that this one needs reattach as well
+  // otherwise we will never rebuild the LayoutTree.

[esprehn, 2017/02/02 23:31:03]

I see what you're missing is a call to host->setChildNeedsReattachLayoutTree()
inside the shadow root creation path. Look at the code inside ElementShadow
addShadowRoot. Youll see it already sets bits like this. You just need to do the
same. Note you probably need code for both v1 and v0 shadow roots.

+  if (needsReattachLayoutTree())
+    markAncestorsWithChildNeedsReattachLayoutTree();
+}
+
+void ShadowRoot::rebuildLayoutTree() {
+  // ShadowRoot doesn't support custom callbacks.
+  DCHECK(!hasCustomStyleCallbacks());
+
+  StyleSharingDepthScope sharingScope(*this);
+
+  clearNeedsReattachLayoutTree();
+  rebuildChildrenLayoutTrees();
   clearChildNeedsReattachLayoutTree();
 }
 
 void ShadowRoot::attachLayoutTree(const AttachContext& context) {
   StyleSharingDepthScope sharingScope(*this);
   DocumentFragment::attachLayoutTree(context);
 }
 
 void ShadowRoot::detachLayoutTree(const AttachContext& context) {
   if (context.clearInvalidation)
@@ skipping 170 matching lines @@
       ostream << "ShadowRootType::Open";
       break;
     case ShadowRootType::Closed:
       ostream << "ShadowRootType::Closed";
       break;
   }
   return ostream;
 }
 
 }  // namespace blink