Enable UMA histogram logger for low memor kill events in ArcMetricsService.

components/arc/metrics/arc_metrics_service.h

Index: components/arc/metrics/arc_metrics_service.h
diff --git a/components/arc/metrics/arc_metrics_service.h b/components/arc/metrics/arc_metrics_service.h
index 72b00373d4e209b3d7a34951f63cbe6d7bfe5fc7..ae3b76411b64891194da2f10a09617fd24b48990 100644
--- a/components/arc/metrics/arc_metrics_service.h
+++ b/components/arc/metrics/arc_metrics_service.h
@@ -12,6 +12,7 @@
 #include "components/arc/arc_bridge_service.h"
 #include "components/arc/arc_service.h"
 #include "components/arc/common/arc_bridge.mojom.h"
+#include "components/arc/metrics/arc_low_memory_killer_monitor.h"
 
 namespace arc {
 
@@ -34,6 +35,8 @@ class ArcMetricsService : public ArcService,
   base::ThreadChecker thread_checker_;
   base::RepeatingTimer timer_;
 
+  ArcLowMemoryKillerMonitor low_memory_killer_minotor_;
+
   // Always keep this the last member of this class to make sure it's the
   // first thing to be destructed.
   base::WeakPtrFactory<ArcMetricsService> weak_ptr_factory_;
@@ -43,4 +46,4 @@ class ArcMetricsService : public ArcService,
 
 }  // namespace arc
 
-#endif  // COMPONENTS_ARC_METRICS_ARC_METRICS_SERVICE_H
+#endif  // COMPONENTS_ARC_METRICS_ARC_METRICS_SERVICE_H