[ios] Moved WebUI provider code to ios/web.

ios/public/provider/web/web_ui_ios_message_handler.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_PUBLIC_PROVIDER_WEB_WEB_UI_IOS_MESSAGE_HANDLER_H_
 #define IOS_PUBLIC_PROVIDER_WEB_WEB_UI_IOS_MESSAGE_HANDLER_H_
 
-#include "base/strings/string16.h"
-
-class GURL;
-
-namespace base {
-class DictionaryValue;
-class ListValue;
-}
-
-namespace web {
-
-class WebUIIOS;
-class WebUIIOSImpl;
-
-// Messages sent from the DOM are forwarded via the WebUIIOS to handler
-// classes. These objects are owned by WebUIIOS and destroyed when the
-// host is destroyed.
-class WebUIIOSMessageHandler {
- public:
-  WebUIIOSMessageHandler() : web_ui_(NULL) {}
-  virtual ~WebUIIOSMessageHandler() {}
-
- protected:
-  // Helper methods:
-
-  // Extract an integer value from a list Value.
-  static bool ExtractIntegerValue(const base::ListValue* value, int* out_int);
-
-  // Extract a floating point (double) value from a list Value.
-  static bool ExtractDoubleValue(const base::ListValue* value,
-                                 double* out_value);
-
-  // Extract a string value from a list Value.
-  static base::string16 ExtractStringValue(const base::ListValue* value);
-
-  // This is where subclasses specify which messages they'd like to handle and
-  // perform any additional initialization. At this point web_ui() will return
-  // the associated WebUIIOS object.
-  virtual void RegisterMessages() = 0;
-
-  // Returns the attached WebUIIOS for this handler.
-  WebUIIOS* web_ui() const { return web_ui_; }
-
-  // Sets the attached WebUIIOS - exposed to subclasses for testing purposes.
-  void set_web_ui(WebUIIOS* web_ui) { web_ui_ = web_ui; }
-
- private:
-  // Provide external classes access to web_ui() and set_web_ui().
-  friend class WebUIIOSImpl;
-
-  WebUIIOS* web_ui_;
-};
-
-}  // namespace web
+// TODO(crbug.com/524467): Remove this file once downstream code is switched to
+// use correct header.
+#include "ios/web/public/webui/web_ui_ios_message_handler.h"
 
 #endif  // IOS_PUBLIC_PROVIDER_WEB_WEB_UI_IOS_MESSAGE_HANDLER_H_