Add Mac memory pressure statistic reporting and consolidate platform code

base/memory/memory_pressure_monitor_chromeos.h

Index: base/memory/memory_pressure_monitor_chromeos.h
diff --git a/base/memory/memory_pressure_monitor_chromeos.h b/base/memory/memory_pressure_monitor_chromeos.h
index 1000f30098792254a851d562000e53746f042916..88dccc9df8e3e16507b7b624d0ecc836af584934 100644
--- a/base/memory/memory_pressure_monitor_chromeos.h
+++ b/base/memory/memory_pressure_monitor_chromeos.h
@@ -101,6 +101,13 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   // gets used to count the number of events since the last event occured.
   int moderate_pressure_repeat_count_;
 
+  // The "Memory.PressureLevel" statistic is recorded every
+  // 5 seconds, but the timer to report "ChromeOS.MemoryPressureLevel"
+  // fires every second. This counter is used to allow reporting
+  // "Memory.PressureLevel" correctly without adding another
+  // timer.
+  int seconds_since_reporting_;
+
   // The thresholds for moderate and critical pressure.
   const int moderate_pressure_threshold_percent_;
   const int critical_pressure_threshold_percent_;