Have window.closed return true when frame is closed.

Source/core/frame/Frame.cpp

Index: Source/core/frame/Frame.cpp
diff --git a/Source/core/frame/Frame.cpp b/Source/core/frame/Frame.cpp
index f647b3e5988b5ed202236a17a12183a39112612d..07dd2cd0db364c7238d2c8189735d76e2e590014 100644
--- a/Source/core/frame/Frame.cpp
+++ b/Source/core/frame/Frame.cpp
@@ -63,6 +63,7 @@ Frame::Frame(FrameClient* client, FrameHost* host, FrameOwner* owner)
     , m_owner(owner)
     , m_client(client)
     , m_remotePlatformLayer(0)
+    , m_hasBeenClosed(false)
 {
     ASSERT(page());
 
@@ -122,6 +123,12 @@ Settings* Frame::settings() const
     return 0;
 }
 
+void Frame::setHasBeenClosed()
+{
+    ASSERT(!m_hasBeenClosed);
+    m_hasBeenClosed = true;
+}
+
 void Frame::setDOMWindow(PassRefPtrWillBeRawPtr<LocalDOMWindow> domWindow)
 {
     if (m_domWindow)