Move AtomNSWindowDelegate to a new file

atom/browser/ui/cocoa/atom_ns_window_delegate.h

@@ -0,0 +1,24 @@
+// Copyright (c) 2018 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef ATOM_BROWSER_UI_COCOA_ATOM_NS_WINDOW_DELEGATE_H_
+#define ATOM_BROWSER_UI_COCOA_ATOM_NS_WINDOW_DELEGATE_H_
+
+#include "ui/views/cocoa/views_nswindow_delegate.h"
+
+namespace atom {
+class NativeWindowMac;
+}
+
+@interface AtomNSWindowDelegate : NSObject<NSWindowDelegate> {
+ @private
+  atom::NativeWindowMac* shell_;
+  bool is_zooming_;
+  int level_;
+  bool is_resizable_;
+}
+- (id)initWithShell:(atom::NativeWindowMac*)shell;
+@end
+
+#endif  // ATOM_BROWSER_UI_COCOA_ATOM_NS_WINDOW_DELEGATE_H_