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..04cb64e60583f0cf308a33ee390b98c6a6913461 100644
--- a/components/arc/metrics/arc_metrics_service.h
+++ b/components/arc/metrics/arc_metrics_service.h
@@ -6,6 +6,7 @@
 #define COMPONENTS_ARC_METRICS_ARC_METRICS_SERVICE_H
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/thread_checker.h"
 #include "base/timer/timer.h"
@@ -15,6 +16,8 @@
 
 namespace arc {
 
+class ArcLowMemoryKillerMonitor;
+
 // Collects information from other ArcServices and send UMA metrics.
 class ArcMetricsService : public ArcService,
                           public ArcBridgeService::Observer {
@@ -34,6 +37,8 @@ class ArcMetricsService : public ArcService,
   base::ThreadChecker thread_checker_;
   base::RepeatingTimer timer_;
 
+  scoped_ptr<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 +48,4 @@ class ArcMetricsService : public ArcService,
 
 }  // namespace arc
 
-#endif  // COMPONENTS_ARC_METRICS_ARC_METRICS_SERVICE_H
+#endif  // COMPONENTS_ARC_METRICS_ARC_METRICS_SERVICE_H