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

components/arc/metrics/arc_low_memory_killer_monitor.cc

Index: components/arc/metrics/arc_low_memory_killer_monitor.cc
diff --git a/chrome/browser/chromeos/arc/arc_low_memory_killer_monitor.cc b/components/arc/metrics/arc_low_memory_killer_monitor.cc
similarity index 91%
rename from chrome/browser/chromeos/arc/arc_low_memory_killer_monitor.cc
rename to components/arc/metrics/arc_low_memory_killer_monitor.cc
index 4976cf085255b745811628f2f831ce7ed3d924b9..2f46fe12fb6087094592cf267bdfe6f4ad5bb93c 100644
--- a/chrome/browser/chromeos/arc/arc_low_memory_killer_monitor.cc
+++ b/components/arc/metrics/arc_low_memory_killer_monitor.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/browser/chromeos/arc/arc_low_memory_killer_monitor.h"
+#include "components/arc/metrics/arc_low_memory_killer_monitor.h"
 
 #include <errno.h>
 #include <fcntl.h>
@@ -72,6 +72,7 @@ void ArcLowMemoryKillerMonitor::Run(
   int64_t timestamp, last_timestamp = -1;
   const TimeDelta kMaxTimeDelta =
       TimeDelta::FromSeconds(MAX_LOWMEMORYKILL_TIME_SECS);
+  int oom_kills = 0;
 
   while (fgets(buf, kMaxBufSize, kmsg_handle)) {
     if (worker_pool->IsShutdownInProgress()) {
@@ -99,11 +100,15 @@ void ArcLowMemoryKillerMonitor::Run(
           time_delta = TimeDelta::FromMicroseconds(timestamp - last_timestamp);
         }
         last_timestamp = timestamp;
+        UMA_HISTOGRAM_LOWMEMORYKILL_TIMES(
+            "Arc.LowMemoryKiller.TimeDelta", time_delta);
+
+        ++oom_kills;
+        UMA_HISTOGRAM_CUSTOM_COUNTS(

[hidehiko, 2016/03/24 08:11:21]

Shouldn't this be out of the while loop?
If it is intentional to count less values than final oom_kills value, it's nice
to comment why.

[cylee1, 2016/03/24 14:36:06]

Yes it's intentional. One of the reason is this dedicated loop may not exit when
shutting down chrome because of the blocking fgets(). As a workaround a
cumulative count should be acceptable. The existing metric
"Tabs.SadTab.KillCreated.OOM" is also cumulative.

+            "Arc.LowMemoryKiller.Count", oom_kills, 1, 1000, 1001);
 
-        UMA_HISTOGRAM_MEMORY_KB("ArcRuntime.LowMemoryKiller.FreedSize",
+        UMA_HISTOGRAM_MEMORY_KB("Arc.LowMemoryKiller.FreedSize",
                                 freed_size);
-        UMA_HISTOGRAM_LOWMEMORYKILL_TIMES(
-            "ArcRuntime.LowMemoryKiller.TimeDelta", time_delta);
       }
     }
   }