Upstream the iOS web_shell and supporting code

ios/web/shell/shell_web_main_parts.h

+// 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_SHELL_WEB_MAIN_PARTS_H_
+#define IOS_WEB_SHELL_SHELL_WEB_MAIN_PARTS_H_
+
+#include "ios/web/public/app/web_main_parts.h"
+
+#include "base/memory/scoped_ptr.h"
+
+namespace web {
+class ShellBrowserState;
+
+// Shell-specific implementation of WebMainParts.
+class ShellWebMainParts : public WebMainParts {
+ public:
+  ShellWebMainParts();
+  ~ShellWebMainParts() override;
+
+  ShellBrowserState* browser_state() const { return browser_state_.get(); }
+
+  // WebMainParts implementation.
+  void PreMainMessageLoopRun() override;
+
+ private:
+  scoped_ptr<ShellBrowserState> browser_state_;
+};
+
+}  // namespace web
+
+#endif  // IOS_WEB_SHELL_SHELL_WEB_MAIN_PARTS_H_