chrome: Cleanup class/struct forward declarations

chrome/browser/performance_monitor/performance_monitor.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_PERFORMANCE_MONITOR_PERFORMANCE_MONITOR_H_
 #define CHROME_BROWSER_PERFORMANCE_MONITOR_PERFORMANCE_MONITOR_H_
 
 #include <map>
 #include <memory>
 #include <vector>
 
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/process/process_handle.h"
 #include "base/timer/timer.h"
 #include "chrome/browser/performance_monitor/process_metrics_history.h"
 
-namespace content {
-struct ChildProcessData;
-}
-
 namespace performance_monitor {
 
 class ProcessMetricsHistory;
 
 // PerformanceMonitor is a tool which periodically monitors performance metrics
 // for histogram logging and possibly taking action upon noticing serious
 // performance degradation.
 class PerformanceMonitor {
  public:
   // Returns the current PerformanceMonitor instance if one exists; otherwise
@@ skipping 37 matching lines @@
 
   // The timer to signal PerformanceMonitor to perform its timed collections.
   base::OneShotTimer repeating_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(PerformanceMonitor);
 };
 
 }  // namespace performance_monitor
 
 #endif  // CHROME_BROWSER_PERFORMANCE_MONITOR_PERFORMANCE_MONITOR_H_