[Mac] Report statistics more regularly in Mac memory pressure monitor

base/memory/memory_pressure_monitor_mac.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_MEMORY_MEMORY_PRESSURE_MONITOR_MAC_H_
 #define BASE_MEMORY_MEMORY_PRESSURE_MONITOR_MAC_H_
 
 #include <CoreFoundation/CFDate.h>
 #include <dispatch/dispatch.h>
 
 #include "base/base_export.h"
 #include "base/mac/scoped_dispatch_object.h"
 #include "base/macros.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/memory_pressure_monitor.h"
 
 namespace base {
 namespace mac {
 
 class TestMemoryPressureMonitor;
 
 // Declares the interface for the Mac MemoryPressureMonitor, which reports
 // memory pressure events and status.
 class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
  public:
   MemoryPressureMonitor();
   ~MemoryPressureMonitor() override;
 
   // Returns the currently-observed memory pressure.
-  MemoryPressureLevel GetCurrentPressureLevel() const override;
+  MemoryPressureLevel GetCurrentPressureLevel() override;
 
   void SetDispatchCallback(const DispatchCallback& callback) override;
 
  private:
   friend TestMemoryPressureMonitor;
 
   static MemoryPressureLevel
       MemoryPressureLevelForMacMemoryPressure(int mac_memory_pressure);
   void OnMemoryPressureChanged(dispatch_source_s* event_source,
                                const DispatchCallback& dispatch_callback);
+  void SendStatisticsIfNecessary(bool pressure_level_changed);
 
   ScopedDispatchObject<dispatch_source_t> memory_level_event_source_;
 
   DispatchCallback dispatch_callback_;
 
-  CFTimeInterval last_pressure_change_;
+  CFTimeInterval last_statistic_report_;
 
   MemoryPressureLevel last_pressure_level_;
 
   // The UMA statistic is recorded in 5 second increments. This
   // accumulates the remaining time to be rolled into the next
   // call.
   CFTimeInterval reporting_error_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);
 };
 
 }  // namespace mac
 }  // namespace base
 
 #endif  // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_MAC_H_