Move Frame pointer to be held by DOMWindow base class.

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

Index: third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
diff --git a/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp b/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
index 483b20d5ed6f419fa04435a6d3172adf5f0bac61..ca0c5bb02e96392783b839587223e3963fce6041 100644
--- a/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
+++ b/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
@@ -272,7 +272,7 @@ bool LocalDOMWindow::allowPopUp() {
 }
 
 LocalDOMWindow::LocalDOMWindow(LocalFrame& frame)
-    : m_frame(&frame),
+    : DOMWindow(frame),
       m_visualViewport(DOMVisualViewport::create(this)),
       m_unusedPreloadsTimer(
           TaskRunnerHelper::get(TaskType::UnspecedTimer, &frame),
@@ -484,7 +484,7 @@ void LocalDOMWindow::frameDestroyed() {
   resetLocation();
   m_properties.clear();
   removeAllEventListeners();
-  m_frame = nullptr;
+  disconnectFromFrame();
 }
 
 void LocalDOMWindow::registerProperty(DOMWindowProperty* property) {
@@ -1607,7 +1607,6 @@ DOMWindow* LocalDOMWindow::open(const String& urlString,
 }
 
 DEFINE_TRACE(LocalDOMWindow) {
-  visitor->trace(m_frame);
   visitor->trace(m_document);
   visitor->trace(m_properties);
   visitor->trace(m_screen);
@@ -1635,12 +1634,4 @@ DEFINE_TRACE_WRAPPERS(LocalDOMWindow) {
   DOMWindow::traceWrappers(visitor);
 }
 
-LocalFrame* LocalDOMWindow::frame() const {
-  // If the LocalDOMWindow still has a frame reference, that frame must point
-  // back to this LocalDOMWindow: otherwise, it's easy to get into a situation
-  // where script execution leaks between different LocalDOMWindows.
-  SECURITY_DCHECK(!m_frame || m_frame->domWindow() == this);
-  return m_frame;
-}
-
 }  // namespace blink