Add metrics for the number of attached displays.

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.h

 // Copyright (c) 2013 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_METRICS_CHROME_BROWSER_MAIN_EXTRA_PARTS_METRICS_H_
 #define CHROME_BROWSER_METRICS_CHROME_BROWSER_MAIN_EXTRA_PARTS_METRICS_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/chrome_browser_main_extra_parts.h"
 
+class ChromeBrowserMainExtraPartsMetricsMac;
 class ChromeBrowserMainParts;
 
 namespace chrome {
 void AddMetricsExtraParts(ChromeBrowserMainParts* main_parts);
 }
 
 class ChromeBrowserMainExtraPartsMetrics : public ChromeBrowserMainExtraParts {
  public:
   ChromeBrowserMainExtraPartsMetrics();
   virtual ~ChromeBrowserMainExtraPartsMetrics();
 
   // Overridden from ChromeBrowserMainExtraParts:
   virtual void PreProfileInit() OVERRIDE;
   virtual void PreBrowserStart() OVERRIDE;
   virtual void PostBrowserStart() OVERRIDE;
 
  private:
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  // This member records OSX specific metrics.
+  scoped_ptr<ChromeBrowserMainExtraPartsMetricsMac> extra_parts_metrics_mac_;
+#endif  // defined(OS_MACOSX) && !defined(OS_IOS)
+
   DISALLOW_COPY_AND_ASSIGN(ChromeBrowserMainExtraPartsMetrics);
 };
 
 #endif  // CHROME_BROWSER_METRICS_CHROME_BROWSER_MAIN_EXTRA_PARTS_METRICS_H_