Use correct document for notifying of inserted import.

third_party/WebKit/Source/core/html/imports/HTMLImportChild.cpp

 /*
  * Copyright (C) 2013 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 29 matching lines @@
 #include "core/html/imports/HTMLImportChildClient.h"
 #include "core/html/imports/HTMLImportLoader.h"
 #include "core/html/imports/HTMLImportTreeRoot.h"
 #include "core/html/imports/HTMLImportsController.h"
 
 namespace blink {
 
 HTMLImportChild::HTMLImportChild(const KURL& url,
                                  HTMLImportLoader* loader,
                                  SyncMode sync)
-    : HTMLImport(sync), m_url(url), m_loader(loader), m_client(nullptr) {}
+    : HTMLImport(sync), m_url(url), m_loader(loader), m_client(nullptr) {
+  DCHECK(loader);
+}
 
 HTMLImportChild::~HTMLImportChild() {}
 
 void HTMLImportChild::ownerInserted() {
   if (!m_loader->isDone())
     return;
-  document()->styleEngine().htmlImportAddedOrRemoved();
+
+  DCHECK(root());
+  DCHECK(root()->document());
+  root()->document()->styleEngine().htmlImportAddedOrRemoved();
   // TODO(rune@opera.com): resolverChanged() can be removed once stylesheet
   // updates are async. https://crbug.com/567021
   root()->document()->styleEngine().resolverChanged(AnalyzedStyleUpdate);
 }
 
 void HTMLImportChild::didShareLoader() {
   createCustomElementMicrotaskStepIfNeeded();
   stateWillChange();
 }
 
@@ skipping 121 matching lines @@
 #endif
 
 DEFINE_TRACE(HTMLImportChild) {
   visitor->trace(m_customElementMicrotaskStep);
   visitor->trace(m_loader);
   visitor->trace(m_client);
   HTMLImport::trace(visitor);
 }
 
 }  // namespace blink