Upstream the iOS web_shell and supporting code

ios/web/public/app/web_main_delegate.h

Index: ios/web/public/app/web_main_delegate.h
diff --git a/ios/web/public/app/web_main_delegate.h b/ios/web/public/app/web_main_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_PUBLIC_APP_WEB_MAIN_DELEGATE_H_
+#define IOS_WEB_PUBLIC_APP_WEB_MAIN_DELEGATE_H_
+
+namespace web {
+
+// Contains delegate hooks that allow a web/ embedder to customize the basic
+// startup and shutdown flow.  This delegate is called very early in startup and
+// very late in shutdown, so only minimal code should be run in its
+// implementation.  WebMainParts will be a more appropriate place for most
+// startup code.
+class WebMainDelegate {
+ public:
+  virtual ~WebMainDelegate() {}
+
+  // Tells the embedder that the absolute basic startup has been done, i.e.
+  // it's now safe to create singletons and check the command line.
+  virtual void BasicStartupComplete() {}
+
+  // Called right before the process exits.
+  // TODO(rohitrao): This may not be used for anything.  Remove if useless.
+  virtual void ProcessExiting() {}
+};
+
+}  // namespace web
+
+#endif  // IOS_WEB_PUBLIC_APP_WEB_MAIN_DELEGATE_H_