chrome: Cleanup class/struct forward declarations

chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.h

 // Copyright (c) 2012 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 CHROME_BROWSER_UI_COCOA_OMNIBOX_OMNIBOX_VIEW_MAC_H_
 #define CHROME_BROWSER_UI_COCOA_OMNIBOX_OMNIBOX_VIEW_MAC_H_
 
 #import <Cocoa/Cocoa.h>
 #include <stddef.h>
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "chrome/browser/ui/cocoa/location_bar/autocomplete_text_field.h"
 #include "components/omnibox/browser/omnibox_view.h"
 #include "components/security_state/core/security_state.h"
 #include "third_party/skia/include/core/SkColor.h"
 
 class CommandUpdater;
 class OmniboxPopupView;
 class Profile;
 
 namespace content {
 class WebContents;
 }
 
-namespace ui {
-class Clipboard;
-}
-
 // Implements OmniboxView on an AutocompleteTextField.
 class OmniboxViewMac : public OmniboxView,
                        public AutocompleteTextFieldObserver {
  public:
   static SkColor BaseTextColorSkia(bool in_dark_mode);
   static NSColor* BaseTextColor(bool in_dark_mode);
   static NSColor* GetSecureTextColor(
       security_state::SecurityLevel security_level,
       bool in_dark_mode);
 
@@ skipping 187 matching lines @@
   // painted. Used to measure omnibox responsiveness with a histogram.
   base::TimeTicks insert_char_time_;
 
   // The time when OnBeforeDrawRect() was called.
   base::TimeTicks draw_rect_start_time_;
 
   DISALLOW_COPY_AND_ASSIGN(OmniboxViewMac);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_OMNIBOX_OMNIBOX_VIEW_MAC_H_