ui: Cleanup class/struct forward declarations

ui/display/manager/display_layout.h

 // Copyright 2016 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_DISPLAY_MANAGER_DISPLAY_LAYOUT_H_
 #define UI_DISPLAY_MANAGER_DISPLAY_LAYOUT_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/strings/string_piece.h"
 #include "ui/display/display_export.h"
 
-namespace base {
-class Value;
-template <typename T> class JSONValueConverter;
-}
-
 namespace display {
 class Display;
 
 // An identifier used to manage display layout in DisplayManager /
 // DisplayLayoutStore.
 using DisplayIdList = std::vector<int64_t>;
 
 using Displays = std::vector<Display>;
 
 // DisplayPlacement specifies where the display (D) is placed relative to
@@ skipping 96 matching lines @@
   static bool ApplyDisplayPlacement(const DisplayPlacement& placement,
                                     Displays* display_list,
                                     int minimum_offset_overlap);
 
   DISALLOW_COPY_AND_ASSIGN(DisplayLayout);
 };
 
 }  // namespace display
 
 #endif  // UI_DISPLAY_MANAGER_DISPLAY_LAYOUT_H_