Upstream the iOS web_shell and supporting code

ios/web/public/app/web_main.h

Index: ios/web/public/app/web_main.h
diff --git a/ios/web/public/app/web_main.h b/ios/web/public/app/web_main.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_PUBLIC_APP_WEB_MAIN_H_
+#define IOS_WEB_PUBLIC_APP_WEB_MAIN_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "ios/web/public/app/web_main_delegate.h"
+
+namespace web {
+class WebMainRunner;
+
+// Contains parameters passed to WebMain.
+struct WebMainParams {
+  explicit WebMainParams(WebMainDelegate* delegate) : delegate(delegate) {}
+
+  WebMainDelegate* delegate;
+};
+
+// Encapsulates any setup and initialization that is needed by common
+// web/ code.  A single instance of this object should be created during app
+// startup (or shortly after launch), and clients must ensure that this object
+// is not destroyed while web/ code is still on the stack.
+//
+// Clients can add custom code to the startup flow by implementing the methods
+// in WebMainDelegate and WebMainParts.
+class WebMain {
+ public:
+  explicit WebMain(const WebMainParams& params);
+  ~WebMain();
+
+ private:
+  scoped_ptr<WebMainRunner> web_main_runner_;
+};
+
+}  // namespace web
+
+#endif  // IOS_WEB_PUBLIC_APP_WEB_MAIN_H_