Don't crash in V8Window::openMethodCustom when called on RemoteDOMWindow.

Source/bindings/core/v8/custom/V8WindowCustom.cpp

Index: Source/bindings/core/v8/custom/V8WindowCustom.cpp
diff --git a/Source/bindings/core/v8/custom/V8WindowCustom.cpp b/Source/bindings/core/v8/custom/V8WindowCustom.cpp
index 12f7827210682ecb740ff74f458ab9f17c74aabe..fdb61c42a79201cf86da04b932e0199fd22b3ac6 100644
--- a/Source/bindings/core/v8/custom/V8WindowCustom.cpp
+++ b/Source/bindings/core/v8/custom/V8WindowCustom.cpp
@@ -234,7 +234,7 @@ void V8Window::toStringMethodCustom(const v8::FunctionCallbackInfo<v8::Value>& i
 
 void V8Window::openMethodCustom(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
-    LocalDOMWindow* impl = toLocalDOMWindow(V8Window::toImpl(info.Holder()));
+    DOMWindow* impl = V8Window::toImpl(info.Holder());
     ExceptionState exceptionState(ExceptionState::ExecutionContext, "open", "Window", info.Holder(), info.GetIsolate());
     if (!BindingSecurity::shouldAllowAccessToFrame(info.GetIsolate(), impl->frame(), exceptionState)) {
         exceptionState.throwIfNeeded();
@@ -251,7 +251,9 @@ void V8Window::openMethodCustom(const v8::FunctionCallbackInfo<v8::Value>& info)
     }
     TOSTRING_VOID(V8StringResource<TreatNullAndUndefinedAsNullString>, windowFeaturesString, info[2]);
 
-    RefPtrWillBeRawPtr<DOMWindow> openedWindow = impl->open(urlString, frameName, windowFeaturesString, callingDOMWindow(info.GetIsolate()), enteredDOMWindow(info.GetIsolate()));
+    // |impl| has to be a LocalDOMWindow, since RemoteDOMWindows wouldn't have
+    // passed the BindingSecurity check above.
+    RefPtrWillBeRawPtr<DOMWindow> openedWindow = toLocalDOMWindow(impl)->open(urlString, frameName, windowFeaturesString, callingDOMWindow(info.GetIsolate()), enteredDOMWindow(info.GetIsolate()));
     if (!openedWindow)
         return;