Revert of IPC::ParamTraits for ui::Event (towards ui::Events over mojo IPC)

ui/events/keycodes/dom/dom_key.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 UI_EVENTS_KEYCODES_DOM3_DOM_KEY_H_
 #define UI_EVENTS_KEYCODES_DOM3_DOM_KEY_H_
 
 #include <stdint.h>
 
 #include "base/logging.h"
-#include "ipc/ipc_param_traits.h"
 
 namespace ui {
 
 // Integer representation of UI Events KeyboardEvent.key value.
 //
 // The semantics follow the web string form[1]: the value is either a
 // Unicode character or one of a defined set of additional values[2].
 // There is one notable difference from the UI Events string key: for
 // the 'Dead' key, this type provides a whole range of values that also
 // encode the associated combining character. (They are not quite the
@@ skipping 119 matching lines @@
   // In the future (cue the theremin) this can be replaced with constexpr
   // functions.
   template<Base C> struct Constant {
     enum : Base {
       Character = TYPE_UNICODE | C,
       Dead = TYPE_DEAD | C,
     };
   };
 
  private:
-  friend struct IPC::ParamTraits<ui::DomKey>;
-
   Base value_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_KEYCODES_DOM3_DOM_KEY_H_