Zero-sized windows are bad.

ui/base/cocoa/window_size_constants.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_BASE_COCOA_WINDOW_SIZE_CONSTANTS_H_
+#define UI_BASE_COCOA_WINDOW_SIZE_CONSTANTS_H_
+#pragma once
+
+#include "ui/base/ui_export.h"
+
+#import <Foundation/Foundation.h>
+
+namespace ui {
+
+// It is not valid to make a zero-sized window. Use this constant instead.
+UI_EXPORT extern const NSRect kWindowSizeDeterminedLater;
+
+}  // namespace ui
+
+#endif  // UI_BASE_COCOA_WINDOW_SIZE_CONSTANTS_H_