Upstream the iOS web_shell and supporting code

ios/web/shell/app_delegate.h

Index: ios/web/shell/app_delegate.h
diff --git a/ios/web/shell/app_delegate.h b/ios/web/shell/app_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..fba25e8a2376211bbe5f0629e79e8d6addaf80f9
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+++ b/ios/web/shell/app_delegate.h
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+// Copyright 2014 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 IOS_WEB_SHELL_APP_DELEGATE_H_
+#define IOS_WEB_SHELL_APP_DELEGATE_H_
+
+#import <UIKit/UIKit.h>
+
+@interface AppDelegate : UIResponder<UIApplicationDelegate>
+
+@property(nonatomic, retain) UIWindow* window;
+
+@end
+
+#endif  // IOS_WEB_SHELL_APP_DELEGATE_H_