blimp: Cleanup class/struct forward declarations

blimp/client/public/contents/blimp_navigation_controller.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_PUBLIC_CONTENTS_BLIMP_NAVIGATION_CONTROLLER_H_
 #define BLIMP_CLIENT_PUBLIC_CONTENTS_BLIMP_NAVIGATION_CONTROLLER_H_
 
 #include "base/macros.h"
 #include "url/gurl.h"
 
 namespace blimp {
 namespace client {
 
-class BlimpContentsObserver;
-
 // The BlimpNavigationController maintains the back-forward list for a
 // BlimpContents and manages all navigation within that list.
 //
 // Each BlimpNavigationController belongs to one BlimpContents, and each
 // BlimpContents has exactly one BlimpNavigationController.
 class BlimpNavigationController {
  public:
   virtual ~BlimpNavigationController() = default;
 
   // Calls to LoadURL informs the engine that it should start navigating to the
@@ skipping 19 matching lines @@
   BlimpNavigationController() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BlimpNavigationController);
 };
 
 }  // namespace client
 }  // namespace blimp
 
 #endif  // BLIMP_CLIENT_PUBLIC_CONTENTS_BLIMP_NAVIGATION_CONTROLLER_H_