ui: Cleanup class/struct forward declarations

ui/views/animation/ink_drop.h

 // Copyright 2015 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_VIEWS_ANIMATION_INK_DROP_H_
 #define UI_VIEWS_ANIMATION_INK_DROP_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "ui/compositor/layer_tree_owner.h"
 #include "ui/events/event_handler.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/views/animation/ink_drop_state.h"
 #include "ui/views/views_export.h"
 
-namespace ui {
-class Layer;
-}
 namespace views {
 
 // Pure virtual base class that manages the lifetime and state of an ink drop
 // ripple as well as visual hover state feedback.
 class VIEWS_EXPORT InkDrop {
  public:
   virtual ~InkDrop() {}
 
   // Gets the target state of the ink drop.
   virtual InkDropState GetTargetInkDropState() const = 0;
@@ skipping 16 matching lines @@
  protected:
   InkDrop() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InkDrop);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_ANIMATION_INK_DROP_H_