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.
+  setNeedsReattachLayoutTree();

[esprehn, 2017/02/02 08:37:10]

This is setting reattach unconditionally on every shadow root which isn't right.
You should never need to force this bit on here.

[nainar, 2017/02/02 23:13:06]

When we call ShadowRoot::recalcStyle() we have no way of knowing when we need to
call ShadowRoot::rebuildLayoutTree() currently only the NeedsReattachLayoutTree
flag is set on the ShadowRoot itself. However it's ancestors dont have this
information. 

I understand that we are indiscriminately calling
ShadowRoot::rebuildLayoutTree() as a result of this. The only other way I see is
to check if the NeedsReattachLayoutTree flag is set and then mark the ancestors
accordingly. Which is the same as calling setNeedsReattachLayoutTree()

+}
+
+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