Add metrics for the number of attached displays.

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.h

Index: chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.h
diff --git a/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.h b/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.h
index 0e4fdbb9efc7aaad7612cd469ab0ee18e957b360..4b859a775616d5f8dfe93b462b36a606ded74a00 100644
--- a/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.h
+++ b/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.h
@@ -10,6 +10,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/chrome_browser_main_extra_parts.h"
 
+class ChromeBrowserMainExtraPartsMetricsMac;
 class ChromeBrowserMainParts;
 
 namespace chrome {
@@ -27,6 +28,11 @@ class ChromeBrowserMainExtraPartsMetrics : public ChromeBrowserMainExtraParts {
   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);
 };