Make External per-window rather than a static Persistent.

third_party/WebKit/Source/core/frame/DOMWindow.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/frame/DOMWindow.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/dom/SecurityContext.h"
@@ skipping 94 matching lines @@
   return parent ? parent->domWindow() : frame()->domWindow();
 }
 
 DOMWindow* DOMWindow::top() const {
   if (!frame())
     return nullptr;
 
   return frame()->tree().top()->domWindow();
 }
 
-External* DOMWindow::external() const {
-  DEFINE_STATIC_LOCAL(Persistent<External>, external, (new External));
-  return external;
+External* DOMWindow::external() {
+  if (!m_external)
+    m_external = new External;
+  return m_external;
 }
 
 DOMWindow* DOMWindow::anonymousIndexedGetter(uint32_t index) const {
   if (!frame())
     return nullptr;
 
   Frame* child = frame()->tree().scopedChild(index);
   return child ? child->domWindow() : nullptr;
 }
 
@@ skipping 304 matching lines @@
   // If we're a top level window, bring the window to the front.
   if (frame()->isMainFrame() && allowFocus)
     page->chromeClient().focus();
 
   page->focusController().focusDocumentView(frame(), true /* notifyEmbedder */);
 }
 
 DEFINE_TRACE(DOMWindow) {
   visitor->trace(m_frame);
   visitor->trace(m_location);
+  visitor->trace(m_external);
   EventTargetWithInlineData::trace(visitor);
 }
 
 }  // namespace blink