Call Element::rebuildLayoutTree from Document::updateStyle directly

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

Index: third_party/WebKit/Source/core/dom/shadow/ShadowRoot.cpp
diff --git a/third_party/WebKit/Source/core/dom/shadow/ShadowRoot.cpp b/third_party/WebKit/Source/core/dom/shadow/ShadowRoot.cpp
index c72f2a0cdc84b8557a6fa137266e55be6b0c5142..d8403b9aa0a6692d94690f27a478a2bfe6d1deb9 100644
--- a/third_party/WebKit/Source/core/dom/shadow/ShadowRoot.cpp
+++ b/third_party/WebKit/Source/core/dom/shadow/ShadowRoot.cpp
@@ -147,10 +147,22 @@ void ShadowRoot::recalcStyle(StyleRecalcChange change) {
 
   // There's no style to update so just calling recalcStyle means we're updated.
   clearNeedsStyleRecalc();
-  clearNeedsReattachLayoutTree();
 
   recalcDescendantStyles(change);
   clearChildNeedsStyleRecalc();
+
+  if (!host().childNeedsReattachLayoutTree())
+    clearNeedsReattachLayoutTree();

[esprehn, 2017/02/15 02:01:00]

this shouldn't be needed, how do we get here with the bits up the tree invalid?

if yourself has needsReattachLayoutTree here then you can
CHECK(host().childNeedsReattachLayoutTree()) or something is bad

[nainar, 2017/02/15 06:04:46]

Given the following test case:

<script>
onload = function() {
    thirdProgress.appendChild(firstProgress);
}
</script>
<progress id="firstProgress">
</progress>
<progress id="thirdProgress"></progress>

If you DCHECK for parentOrShadowHostNode()->childNeedsReattachLayoutTree() in
the case where needsReattachLayoutTree() is true. The assert fails. 

Print debugging shows the following:
When we call thirdProgress.appendChild(firstProgress) we call
ContainerNode::removeBetween() which detaches. Which sets the
NeedsReattachLayoutTree which the parent nodes aren't aware of. 

Which needs to be corrected. Which is why I was trying to do here. 

+}
+
+void ShadowRoot::rebuildLayoutTree() {
+  // ShadowRoot doesn't support custom callbacks.
+  DCHECK(!hasCustomStyleCallbacks());
+
+  StyleSharingDepthScope sharingScope(*this);
+
+  clearNeedsReattachLayoutTree();
+  rebuildChildrenLayoutTrees();
   clearChildNeedsReattachLayoutTree();
 }