Remove CWV class and move setting User Agent to CWVWebViewConfiguration.

ios/web_view/internal/cwv_web_view_configuration_internal.h

 // Copyright 2017 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_VIEW_INTERNAL_CWV_WEB_VIEW_CONFIGURATION_INTERNAL_H_
 #define IOS_WEB_VIEW_INTERNAL_CWV_WEB_VIEW_CONFIGURATION_INTERNAL_H_
 
 #import "ios/web_view/public/cwv_web_view_configuration.h"
 
 namespace ios_web_view {
 class WebViewBrowserState;
+class WebViewWebClient;
 }  // namespace ios_web_view
 
 @interface CWVWebViewConfiguration ()
 
 // The browser state associated with this configuration.
 @property(nonatomic, readonly, nonnull)
     ios_web_view::WebViewBrowserState* browserState;
 
+// Returns the web client, setting up the WebMainDelegate and WebMain if needed.
++ (nonnull ios_web_view::WebViewWebClient*)webClient;
+
 @end
 
 #endif  // IOS_WEB_VIEW_INTERNAL_CWV_WEB_VIEW_CONFIGURATION_INTERNAL_H_