Added memory pressure monitor for linux.

base/memory/memory_pressure_monitor_mac.cc

 // 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.
 
-#include "base/memory/memory_pressure_monitor_mac.h"
+#include "base/memory/memory_pressure_monitor.h"
 
 #include <dlfcn.h>
 #include <sys/sysctl.h>
 
 #include "base/mac/mac_util.h"
 
 namespace base {
-namespace mac {
 
 MemoryPressureListener::MemoryPressureLevel
 MemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressure(
     int mac_memory_pressure) {
   switch (mac_memory_pressure) {
     case DISPATCH_MEMORYPRESSURE_NORMAL:
       return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
     case DISPATCH_MEMORYPRESSURE_WARN:
       return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE;
     case DISPATCH_MEMORYPRESSURE_CRITICAL:
       return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL;
   }
   return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
 }
 
 void MemoryPressureMonitor::NotifyMemoryPressureChanged(
     dispatch_source_s* event_source) {
   int mac_memory_pressure = dispatch_source_get_data(event_source);
   MemoryPressureListener::MemoryPressureLevel memory_pressure_level =
       MemoryPressureLevelForMacMemoryPressure(mac_memory_pressure);
   MemoryPressureListener::NotifyMemoryPressure(memory_pressure_level);
 }
 
 MemoryPressureMonitor::MemoryPressureMonitor()
   : memory_level_event_source_(nullptr) {
+  DCHECK(!g_monitor);
+  g_monitor = this;
+
   // _dispatch_source_type_memorypressure is not available prior to 10.9.
   dispatch_source_type_t dispatch_source_memorypressure =
       static_cast<dispatch_source_type_t>
           (dlsym(RTLD_NEXT, "_dispatch_source_type_memorypressure"));
   if (dispatch_source_memorypressure) {
     // The MemoryPressureListener doesn't want to know about transitions to
     // MEMORY_PRESSURE_LEVEL_NONE so don't watch for
     // DISPATCH_MEMORYPRESSURE_NORMAL notifications.
     memory_level_event_source_.reset(
         dispatch_source_create(dispatch_source_memorypressure, 0,
                                DISPATCH_MEMORYPRESSURE_WARN |
                                    DISPATCH_MEMORYPRESSURE_CRITICAL,
                                dispatch_get_global_queue(
                                    DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)));
 
     dispatch_source_set_event_handler(memory_level_event_source_.get(), ^{
         NotifyMemoryPressureChanged(memory_level_event_source_.get());
     });
     dispatch_retain(memory_level_event_source_.get());
     dispatch_resume(memory_level_event_source_.get());
   }
 }
 
 MemoryPressureMonitor::~MemoryPressureMonitor() {
+  DCHECK(g_monitor);
+  g_monitor = nullptr;
 }
 
 MemoryPressureListener::MemoryPressureLevel
 MemoryPressureMonitor::GetCurrentPressureLevel() const {
   if (base::mac::IsOSMountainLionOrEarlier()) {
     return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
   }
   int mac_memory_pressure;
   size_t length = sizeof(int);
   sysctlbyname("kern.memorystatus_vm_pressure_level", &mac_memory_pressure,
                &length, nullptr, 0);
   return MemoryPressureLevelForMacMemoryPressure(mac_memory_pressure);
 }
 
-}  // namespace mac
 }  // namespace base