implement user agent override option.

ios/web/public/navigation_manager.h

 // Copyright 2013 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_NAVIGATION_MANAGER_H_
 #define IOS_WEB_PUBLIC_NAVIGATION_MANAGER_H_
 
 #include <stddef.h>
 
 #import "base/mac/scoped_nsobject.h"
@@ skipping 12 matching lines @@
 class NavigationItem;
 class WebState;
 
 // A NavigationManager maintains the back-forward list for a WebState and
 // manages all navigation within that list.
 //
 // Each NavigationManager belongs to one WebState; each WebState has
 // exactly one NavigationManager.
 class NavigationManager {
  public:
+  // User agent override option used in LoadURLParams.
+  enum class UserAgentOverrideOption : short {
+    // Inherit the user agent type from the last committed non-app specific item

[Eugene But (OOO till 7-30), 2017/03/30 19:21:24]

What if there are no committed items?

[liaoyuke, 2017/03/30 19:56:25]

Done. 

+    // in the NavigationManager.
+    INHERIT = 0,
+
+    // Use the mobile user agent.
+    MOBILE,
+
+    // Use the desktop user agent.
+    DESKTOP

[Eugene But (OOO till 7-30), 2017/03/30 19:21:24]

Optional nit: it's a good practice to have comma after last item. Sp the future
changes will not touch this line.

[liaoyuke, 2017/03/30 19:56:25]

Done.

+  };
+
   // Parameters for URL loading. Most parameters are optional, and can be left
   // at the default values set by the constructor.
   struct WebLoadParams {
    public:
     // The URL to load. Must be set.
     GURL url;
 
     // The referrer for the load. May be empty.
     Referrer referrer;
 
     // The transition type for the load. Defaults to PAGE_TRANSITION_LINK.
     ui::PageTransition transition_type;
 
+    // The user agent override option for the load. Defualts to INHERIT.
+    UserAgentOverrideOption user_agent_override_option;
+
     // True for renderer-initiated navigations. This is
     // important for tracking whether to display pending URLs.
     bool is_renderer_initiated;
 
     // Any extra HTTP headers to add to the load.
     base::scoped_nsobject<NSDictionary> extra_headers;
 
     // Any post data to send with the load. When setting this, you should
     // generally set a Content-Type header as well.
     base::scoped_nsobject<NSData> post_data;
@@ skipping 116 matching lines @@
   // This ignores any pending or transient entries in |source|.  This will be a
   // no-op if called while CanPruneAllButLastCommittedItem() is false.
   virtual void CopyStateFromAndPrune(const NavigationManager* source) = 0;
 
   // Whether the NavigationManager can prune all but the last committed item.
   // This is true when all the following conditions are met:
   // - There is a last committed NavigationItem.
   // - There is no pending history navigation.
   // - There is no transient NavigationItem.
   virtual bool CanPruneAllButLastCommittedItem() const = 0;
-
-  // Forces the pending item to be loaded using desktop user agent. Note that
-  // the pending item may or may not already exist.
-  // TODO(crbug.com/692303): Remove this when overriding the user agent doesn't
-  // create a new NavigationItem.
-  virtual void OverrideDesktopUserAgentForNextPendingItem() = 0;
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_NAVIGATION_MANAGER_H_