[Bindings] Add DCHECK to confirm RemoteWindowProxy is not used for main frame

third_party/WebKit/Source/bindings/core/v8/RemoteWindowProxy.cpp

Index: third_party/WebKit/Source/bindings/core/v8/RemoteWindowProxy.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/RemoteWindowProxy.cpp b/third_party/WebKit/Source/bindings/core/v8/RemoteWindowProxy.cpp
index b484ebebf77af1fdef5e85805b71e2726b195a3d..510b22c2e8740273583bffddc98a4c468c84a8d6 100644
--- a/third_party/WebKit/Source/bindings/core/v8/RemoteWindowProxy.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/RemoteWindowProxy.cpp
@@ -47,7 +47,9 @@ namespace blink {
 RemoteWindowProxy::RemoteWindowProxy(v8::Isolate* isolate,
                                      RemoteFrame& frame,
                                      RefPtr<DOMWrapperWorld> world)
-    : WindowProxy(isolate, frame, std::move(world)) {}
+    : WindowProxy(isolate, frame, std::move(world)) {
+  DCHECK(!this->frame()->isMainFrame());
+}
 
 void RemoteWindowProxy::disposeContext(GlobalDetachmentBehavior behavior) {
   if (m_lifecycle != Lifecycle::ContextInitialized)