Adds an iOS implementation of base::SystemMonitor.

base/system_monitor/system_monitor_ios.mm

Index: base/system_monitor/system_monitor_ios.mm
diff --git a/base/system_monitor/system_monitor_ios.mm b/base/system_monitor/system_monitor_ios.mm
new file mode 100644
index 0000000000000000000000000000000000000000..f3251b60f143c0b119fdcce7323dedab2e60be5f
--- /dev/null
+++ b/base/system_monitor/system_monitor_ios.mm
@@ -0,0 +1,40 @@
+// Copyright (c) 2012 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/system_monitor/system_monitor.h"
+
+#import <UIKit/UIKit.h>
+
+namespace base {
+
+void SystemMonitor::PlatformInit() {
+  NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
+  id foreground =
+      [nc addObserverForName:UIApplicationWillEnterForegroundNotification
+                      object:nil
+                       queue:nil
+                  usingBlock:^(NSNotification* notification) {
+                      ProcessPowerMessage(RESUME_EVENT);
+                  }];
+  id background =
+      [nc addObserverForName:UIApplicationDidEnterBackgroundNotification
+                      object:nil
+                       queue:nil
+                  usingBlock:^(NSNotification* notification) {
+                      ProcessPowerMessage(SUSPEND_EVENT);
+                  }];
+  notification_observers_.push_back(foreground);
+  notification_observers_.push_back(background);
+}
+
+void SystemMonitor::PlatformDestroy() {
+  NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
+  for (std::vector<id>::iterator it = notification_observers_.begin();
+       it != notification_observers_.end(); ++it) {
+    [nc removeObserver:*it];
+  }
+  notification_observers_.clear();
+}
+
+}  // namespace base