SystemMonitor refactoring: move power state monitor into a separate class called PowerMonitor

base/power_monitor/power_monitor_mac.mm

Index: base/power_monitor/power_monitor_mac.mm
diff --git a/base/system_monitor/system_monitor_mac.mm b/base/power_monitor/power_monitor_mac.mm
similarity index 76%
rename from base/system_monitor/system_monitor_mac.mm
rename to base/power_monitor/power_monitor_mac.mm
index d0dbaabcd4417864b21166e81c068e20c769cbe6..aa949db21e0f869e14c64c64e476b2c80bc85cbb 100644
--- a/base/system_monitor/system_monitor_mac.mm
+++ b/base/power_monitor/power_monitor_mac.mm
@@ -5,13 +5,19 @@
 // Implementation based on sample code from
 // http://developer.apple.com/library/mac/#qa/qa1340/_index.html.
 
-#include "base/system_monitor/system_monitor.h"
+#include "base/power_monitor/power_monitor.h"
 
 #include <IOKit/pwr_mgt/IOPMLib.h>
 #include <IOKit/IOMessage.h>
 
 namespace base {
 
+// A helper function as a friend function of PowerMonitor.
+void ProcessPowerEventHelper(PowerMonitor::PowerEvent power_event) {
+  PowerMonitor* power_monitor = PowerMonitor::GetInstance();
+  power_monitor->ProcessPowerEvent(power_event);
+}
+
 namespace {
 
 io_connect_t g_system_power_io_port = 0;
@@ -22,17 +28,15 @@ void SystemPowerEventCallback(void*,
                               io_service_t service,
                               natural_t message_type,
                               void* message_argument) {
-  SystemMonitor* sys_monitor = SystemMonitor::Get();
-  DCHECK(sys_monitor);
   switch (message_type) {
     case kIOMessageSystemWillSleep:
-      sys_monitor->ProcessPowerMessage(SystemMonitor::SUSPEND_EVENT);
+      ProcessPowerEventHelper(PowerMonitor::SUSPEND_EVENT);
       IOAllowPowerChange(g_system_power_io_port,
           reinterpret_cast<intptr_t>(message_argument));
       break;
 
     case kIOMessageSystemWillPowerOn:
-      sys_monitor->ProcessPowerMessage(SystemMonitor::RESUME_EVENT);
+      ProcessPowerEventHelper(PowerMonitor::RESUME_EVENT);
       break;
   }
 }
@@ -45,8 +49,9 @@ void SystemPowerEventCallback(void*,
 // See crbug.com/83783 .
 
 // static
-void SystemMonitor::AllocateSystemIOPorts() {
-  DCHECK_EQ(g_system_power_io_port, 0u);
+void PowerMonitor::AllocateSystemIOPorts() {
+  if (g_system_power_io_port != 0u)

[Hongbo Min, 2012/10/16 14:14:40]

base/power_monitor/power_monitor_mac.mm:53: if (g_system_power_io_port != 0u)
Here I removed the DCHECK_EQ stmt because AllocateSystemIOPorts is designed to
be called once, otherwise, the g_system_power_io_port will be leaked without
IOServiceClose calling when AllocateSystemSystemIOPorts is called multiple
times.

If the AllocateSystemIOPort was ever called and so g_system_power_io_port is
retrieved correctly, we just returns the value got already immediately.

[vandebo (ex-Chrome), 2012/10/16 18:50:16]

Hmm, this is a consequence of changing it to a Singleton. I'm not happy with the
extra changes that have to be made, but it's not too bad either.  I'll defer to
Will on this one.

[willchan no longer on Chromium, 2012/10/16 20:32:37]

I'm confused. Why is this better than before? Let me restate my understanding.
Before:
* Asserts in debug mode if this is ever called more than once.
* Leaks in release mode if this is ever called more than once.

After:
* Gracefully handles calling it more than once.

I think it's a bug to call it more than once and would prefer to catch it. I do
think it's an improvement to gracefully handle it in release mode, but it'd be
great to keep the DCHECK there for debug mode to prevent people from calling
this multiple times.

[vandebo (ex-Chrome), 2012/10/16 23:55:09]

Maybe this and the other issue is why it wasn't a Singleton before... As a
Singleton it's created once per test binary.  However, the test instance will
call AllocateSystemIOPorts once per test.

+    return;
 
   // Notification port allocated by IORegisterForSystemPower.
 
@@ -57,12 +62,10 @@ void SystemMonitor::AllocateSystemIOPorts() {
   DCHECK_NE(g_system_power_io_port, 0u);
 }
 
-void SystemMonitor::PlatformInit() {
-  // Need to call AllocateSystemIOPorts() before constructing a SystemMonitor
+void PowerMonitor::PlatformInit() {
+  // Need to call AllocateSystemIOPorts() before creating a PowerMonitor
   // object.
-  DCHECK_NE(g_system_power_io_port, 0u);
-  if (g_system_power_io_port == 0)
-    return;
+  CHECK_NE(g_system_power_io_port, 0u);
 
   // Add the notification port to the application runloop
   CFRunLoopAddSource(
@@ -71,10 +74,9 @@ void SystemMonitor::PlatformInit() {
       kCFRunLoopCommonModes);
 }
 
-void SystemMonitor::PlatformDestroy() {
-  DCHECK_NE(g_system_power_io_port, 0u);
-  if (g_system_power_io_port == 0)
-    return;
+
+void PowerMonitor::PlatformDestroy() {
+  CHECK_NE(g_system_power_io_port, 0u);
 
   // Remove the sleep notification port from the application runloop
   CFRunLoopRemoveSource(