blimp: Cleanup class/struct forward declarations

blimp/client/core/contents/blimp_navigation_controller_impl.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 BLIMP_CLIENT_CORE_CONTENTS_BLIMP_NAVIGATION_CONTROLLER_IMPL_H_
 #define BLIMP_CLIENT_CORE_CONTENTS_BLIMP_NAVIGATION_CONTROLLER_IMPL_H_
 
 #include "base/macros.h"
 #include "blimp/client/core/contents/navigation_feature.h"
 #include "blimp/client/public/contents/blimp_navigation_controller.h"
 #include "url/gurl.h"
 
 class SkBitmap;
 
 namespace blimp {
 namespace client {
 
-class BlimpContentsObserver;
 class BlimpNavigationControllerDelegate;
 
 class BlimpNavigationControllerImpl
     : public BlimpNavigationController,
       public NavigationFeature::NavigationFeatureDelegate {
  public:
   // The life time of |feature| must remain valid throughout |this|.
   BlimpNavigationControllerImpl(int blimp_contents_id,
                                 BlimpNavigationControllerDelegate* delegate,
                                 NavigationFeature* feature);
@@ skipping 35 matching lines @@
   // Title of the currently active page.
   std::string current_title_;
 
   DISALLOW_COPY_AND_ASSIGN(BlimpNavigationControllerImpl);
 };
 
 }  // namespace client
 }  // namespace blimp
 
 #endif  // BLIMP_CLIENT_CORE_CONTENTS_BLIMP_NAVIGATION_CONTROLLER_IMPL_H_