Add UMA stats to get the quality of service of memory pressure handling scheme in ChromeOS.

base/chromeos/memory_pressure_observer_chromeos.cc

Index: base/chromeos/memory_pressure_observer_chromeos.cc
diff --git a/base/chromeos/memory_pressure_observer_chromeos.cc b/base/chromeos/memory_pressure_observer_chromeos.cc
index 8112c761e5e713e747cb015d8226e62a754c87a8..2f132c24564c14f5b0b825300474ce388f2525e4 100644
--- a/base/chromeos/memory_pressure_observer_chromeos.cc
+++ b/base/chromeos/memory_pressure_observer_chromeos.cc
@@ -5,6 +5,7 @@
 #include "base/chromeos/memory_pressure_observer_chromeos.h"
 
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/process/process_metrics.h"
 #include "base/time/time.h"
 
@@ -74,11 +75,32 @@ MemoryPressureObserverChromeOS::MemoryPressureObserverChromeOS(
           GetModerateMemoryThresholdInPercent(thresholds)),
       critical_pressure_threshold_percent_(
           GetCriticalMemoryThresholdInPercent(thresholds)),
+      time_non_critical_pressure_(0),
+      time_critical_pressure_(0),
       weak_ptr_factory_(this) {
   StartObserving();
 }
 
 MemoryPressureObserverChromeOS::~MemoryPressureObserverChromeOS() {
+  // Record quality of service of memory pressure handling scheme in ChromeOS.
+  // 1 day (approximately in Millisecond) is a good enough upper limit.
+  const int kMaxQualityOfPressureHandleService = 100000000;
+  if (time_critical_pressure_ != 0) {
+    int ratio = time_non_critical_pressure_ / time_critical_pressure_;
+    ratio = (ratio > kMaxQualityOfPressureHandleService)
+                ? kMaxQualityOfPressureHandleService
+                : ratio;
+    UMA_HISTOGRAM_CUSTOM_COUNTS(
+        "ChromeOS.MemoryPressureHandleQuality.TimeRatio", ratio,
+        kMemoryPressureIntervalMs, kMaxQualityOfPressureHandleService, 50);
+  } else {
+    UMA_HISTOGRAM_CUSTOM_COUNTS(
+        "ChromeOS.MemoryPressureHandleQuality.TimeRatio",
+        kMaxQualityOfPressureHandleService, kMemoryPressureIntervalMs,
+        kMaxQualityOfPressureHandleService, 50);
+  }
+  time_non_critical_pressure_ = 0;
+  time_critical_pressure_ = 0;
   StopObserving();
 }
 
@@ -108,6 +130,13 @@ void MemoryPressureObserverChromeOS::CheckMemoryPressure() {
       GetMemoryPressureLevelFromFillLevel(GetUsedMemoryInPercent(),
                                           moderate_pressure_threshold_percent_,
                                           critical_pressure_threshold_percent_);
+
+  if (current_memory_pressure_level_ ==
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL)

[Mr4D (OOO till 08-26), 2015/01/27 13:49:42]

Instead of adding the ms value here, you should remember the time stamp at event
time and subtract them to get the real time delta.

Reason:
The time between events is "roughly" what we are asking for, but in the end the
task scheduler and many other factors decide when / how this is called and the
error is cumulative.

+    time_critical_pressure_ += kMemoryPressureIntervalMs;
+  else
+    time_non_critical_pressure_ += kMemoryPressureIntervalMs;
+
   // In case there is no memory pressure we do not notify.
   if (current_memory_pressure_level_ ==
       MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE) {