[ES6 modules] accessing document.currentScript on module scripts should not crash

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
@@ skipping 5271 matching lines @@
     UseCounter::Count(*this, osd_disposition);
 
     return link_element->Href();
   }
 
   return KURL();
 }
 
 void Document::currentScriptForBinding(
     HTMLScriptElementOrSVGScriptElement& script_element) const {
-  if (!current_script_stack_.IsEmpty())
-    current_script_stack_.back()->SetScriptElementForBinding(script_element);
+  if (!current_script_stack_.IsEmpty()) {
+    if (ScriptElementBase* script_element_base = current_script_stack_.back())
+      script_element_base->SetScriptElementForBinding(script_element);
+  }
 }
 
 void Document::PushCurrentScript(ScriptElementBase* new_current_script) {
   current_script_stack_.push_back(new_current_script);
 }
 
 void Document::PopCurrentScript(ScriptElementBase* script) {
   DCHECK(!current_script_stack_.IsEmpty());
   DCHECK_EQ(current_script_stack_.back(), script);
   current_script_stack_.pop_back();
@@ skipping 1475 matching lines @@
 }
 
 void showLiveDocumentInstances() {
   WeakDocumentSet& set = liveDocumentSet();
   fprintf(stderr, "There are %u documents currently alive:\n", set.size());
   for (blink::Document* document : set)
     fprintf(stderr, "- Document %p URL: %s\n", document,
             document->Url().GetString().Utf8().data());
 }
 #endif