cc: Cleanup class/struct forward declarations

cc/debug/invalidation_benchmark.h

 // Copyright 2014 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 CC_DEBUG_INVALIDATION_BENCHMARK_H_
 #define CC_DEBUG_INVALIDATION_BENCHMARK_H_
 
 #include <stdint.h>
 
 #include <string>
 
 #include "cc/debug/micro_benchmark_controller.h"
 
 namespace cc {
 
 class LayerTree;
-class Layer;
+
 // NOTE: this benchmark will not measure or return any results, it will simply
 // invalidate a certain area of each layer every frame. It is intended to be
 // used in combination with a telemetry benchmark that does the actual
 // measurement.
 class CC_EXPORT InvalidationBenchmark : public MicroBenchmark {
  public:
   explicit InvalidationBenchmark(std::unique_ptr<base::Value> value,
                                  const MicroBenchmark::DoneCallback& callback);
   ~InvalidationBenchmark() override;
 
   // Implements MicroBenchmark interface.
   void DidUpdateLayers(LayerTree* layer_tree) override;
   void RunOnLayer(PictureLayer* layer) override;
   bool ProcessMessage(std::unique_ptr<base::Value> value) override;
 
  private:
   enum Mode { FIXED_SIZE, LAYER, VIEWPORT, RANDOM };
 
   float LCGRandom();
 
   Mode mode_;
   int width_;
   int height_;
   uint32_t seed_;
 };
 
 }  // namespace cc
 
 #endif  // CC_DEBUG_INVALIDATION_BENCHMARK_H_