Move power event handling logic from ui/ to base/ on Windows

base/system_monitor/system_monitor.h

 // 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.
 
 #ifndef BASE_SYSTEM_MONITOR_SYSTEM_MONITOR_H_
 #define BASE_SYSTEM_MONITOR_SYSTEM_MONITOR_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 116 matching lines @@
   // Remove an existing observer.
   // Can be called from any thread.
   // Must not be called from within a notification callback.
   void RemovePowerObserver(PowerObserver* obs);
   void RemoveDevicesChangedObserver(DevicesChangedObserver* obs);
 
   // The ProcessFoo() style methods are a broken pattern and should not
   // be copied. Any significant addition to this class is blocked on
   // refactoring to improve the state of affairs. See http://crbug.com/149059
 
-#if defined(OS_WIN)
-  // Windows-specific handling of a WM_POWERBROADCAST message.
-  // Embedders of this API should hook their top-level window
-  // message loop and forward WM_POWERBROADCAST through this call.
-  void ProcessWmPowerBroadcastMessage(int event_id);
-#endif
-
   // Cross-platform handling of a power event.
   void ProcessPowerMessage(PowerEvent event_id);
 
   // Cross-platform handling of a device change event.
   void ProcessDevicesChanged(DeviceType device_type);
 
  private:
+#if defined(OS_WIN)
+  // Represents a message-only window for power message handling on Windows.
+  // Only allow SystemMonitor to create it.
+  class PowerMessageWindow {

[Hongbo Min, 2013/02/23 03:42:01]

Let me explain the reason why we need to define the class in the header file.

If we use forwarding declaration in combination with scoped_ptr, and define the
class in system_monitor_win.cc file, we will get compiling error saying 'use
undefined type" when compiling system_monitor.cc file. The scoped_ptr usage
can't span over 2 translation units (system_monitor.cc and
system_monitor_win.cc). 

It can be solved by defining the class in system_monitor.cc file, however, it is
still not a good idea to define a platform-specific class in the
system_monitor.cc, not in the system_monitor_win.cc.

[vandebo (ex-Chrome), 2013/02/25 17:46:54]

I see.  This can be solved by making SystemMonitor a base class and putting the
implementation in platform specific classes that inherit from SystemMonitor. 
But that can be done later.

+   public:
+    PowerMessageWindow();
+    ~PowerMessageWindow();
+
+   private:
+    void ProcessWmPowerBroadcastMessage(int event_id);
+    LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
+                             WPARAM wparam, LPARAM lparam);
+    static LRESULT CALLBACK WndProcThunk(HWND hwnd,
+                                         UINT message,
+                                         WPARAM wparam,
+                                         LPARAM lparam);
+    // Instance of the module containing the window procedure.
+    HMODULE instance_;
+    // A hidden message-only window.
+    HWND message_hwnd_;
+  };
+#endif
+
 #if defined(OS_MACOSX)
   void PlatformInit();
   void PlatformDestroy();
 #endif
 
   // Platform-specific method to check whether the system is currently
   // running on battery power.  Returns true if running on batteries,
   // false otherwise.
   bool IsBatteryPower();
 
@@ skipping 15 matching lines @@
 
 #if defined(ENABLE_BATTERY_MONITORING)
   base::OneShotTimer<SystemMonitor> delayed_battery_check_;
 #endif
 
 #if defined(OS_IOS)
   // Holds pointers to system event notification observers.
   std::vector<id> notification_observers_;
 #endif
 
+#if defined(OS_WIN)
+  PowerMessageWindow power_message_window_;
+#endif
+
   DISALLOW_COPY_AND_ASSIGN(SystemMonitor);
 };
 
 }  // namespace base
 
 #endif  // BASE_SYSTEM_MONITOR_SYSTEM_MONITOR_H_