Add metrics for the number of attached displays.

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc

Index: chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
diff --git a/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc b/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
index 64c01a71f77087d0d41986768434f9542925975b..4b51933cde08a205fd23f942eb13c9991f12c235 100644
--- a/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
+++ b/chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc
@@ -38,6 +38,10 @@
 #include "chrome/installer/util/google_update_settings.h"
 #endif  // defined(OS_WIN)
 
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+#include "chrome/browser/metrics/chrome_browser_main_extra_parts_metrics_mac.h"
+#endif  // defined(OS_MACOSX) && !defined(OS_IOS)
+
 namespace {
 
 enum UMALinuxGlibcVersion {
@@ -243,6 +247,10 @@ void ChromeBrowserMainExtraPartsMetrics::PostBrowserStart() {
 #endif
   RecordTouchEventState();
 
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  extra_parts_metrics_mac_.reset(new ChromeBrowserMainExtraPartsMetricsMac);
+#endif  // defined(OS_MACOSX) && !defined(OS_IOS)
+
   const int kStartupMetricsGatheringDelaySeconds = 45;
   content::BrowserThread::GetBlockingPool()->PostDelayedTask(
       FROM_HERE,