chrome: Cleanup class/struct forward declarations

chrome/browser/gpu/gpu_feature_checker.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_GPU_GPU_FEATURE_CHECKER_H_
 #define CHROME_BROWSER_GPU_GPU_FEATURE_CHECKER_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "content/public/browser/gpu_data_manager_observer.h"
 #include "gpu/config/gpu_feature_type.h"
 
-namespace content {
-class GpuDataManager;
-}  // namespace content
-
 class GPUFeatureChecker : public base::RefCountedThreadSafe<GPUFeatureChecker>,
                           public content::GpuDataManagerObserver {
  public:
   typedef base::Callback<void(bool feature_available)> FeatureAvailableCallback;
 
   GPUFeatureChecker(gpu::GpuFeatureType feature,
                     FeatureAvailableCallback callback);
 
   // Check to see if |feature_| is available on the current GPU. |callback_|
   // will be called to indicate the availability of the feature. Must be called
   // from the the UI thread.
   void CheckGPUFeatureAvailability();
 
   // content::GpuDataManagerObserver
   void OnGpuInfoUpdate() override;
 
  private:
   friend class base::RefCountedThreadSafe<GPUFeatureChecker>;
 
   ~GPUFeatureChecker() override;
 
   gpu::GpuFeatureType feature_;
   FeatureAvailableCallback callback_;
 
   DISALLOW_COPY_AND_ASSIGN(GPUFeatureChecker);
 };
 
 #endif  // CHROME_BROWSER_GPU_GPU_FEATURE_CHECKER_H_