Make setNeedsActiveStyleUpdate mark treescope dirty only.

third_party/WebKit/Source/core/html/HTMLLinkElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLLinkElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLLinkElement.cpp b/third_party/WebKit/Source/core/html/HTMLLinkElement.cpp
index 06a8129631ec454bb9090660d522cbdf78bc5917..f72cfd5292d9634b26b3d2297b66e1f6e38b6d6b 100644
--- a/third_party/WebKit/Source/core/html/HTMLLinkElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLLinkElement.cpp
@@ -218,13 +218,13 @@ void HTMLLinkElement::removedFrom(ContainerNode* insertionPoint) {
   }
   document().styleEngine().removeStyleSheetCandidateNode(*this);
 
-  StyleSheet* removedSheet = sheet();
-
   if (m_link)
     m_link->ownerRemoved();
 
-  document().styleEngine().setNeedsActiveStyleUpdate(removedSheet,
-                                                     FullStyleUpdate);
+  document().styleEngine().setNeedsActiveStyleUpdate(treeScope());

[meade_UTC10, 2016/12/05 23:57:22]

It looks like the treeScope is not yet registered in the StyleEngine, which is
why the DCHECK I commented on is getting hit. Do you need to call 
document().styleEngine().styleSheetsForStyleSheetList(treeScope()) or 
move this call to before line 219?

[rune, 2016/12/06 14:53:22]

It's the wrong treeScope(), we should have found the right ShadowRoot treeScope
for the removeStyleSheetCandidateNode(). I don't think we even need the
setNeedsActiveStyleUpdate call here since removeStyleSheetCandidateNode will do
that for us.

Anyway, needed to fix https://crbug.com/671596 first:

https://codereview.chromium.org/2551973003/

+  // TODO(rune@opera.com): resolverChanged() can be removed once stylesheet
+  // updates are async. https://crbug.com/567021
+  document().styleEngine().resolverChanged(FullStyleUpdate);
 }
 
 void HTMLLinkElement::finishParsingChildren() {