Implement PowerSaveBlocker2 for Linux. Much simpler than the original!

content/browser/power_save_blocker.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 CONTENT_BROWSER_POWER_SAVE_BLOCKER_H_
 #define CONTENT_BROWSER_POWER_SAVE_BLOCKER_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 42 matching lines @@
   static int blocker_count_[];
 
   DISALLOW_COPY_AND_ASSIGN(PowerSaveBlocker);
 };
 
 namespace content {
 
 // NOT READY YET. PowerSaveBlocker above is soon to be replaced by this class,
 // but it's not done yet so client code should use the one above for now.
 // A RAII-style class to block the system from entering low-power (sleep) mode.
+// This class is thread-safe; it may be constructed and deleted on any thread.
 class CONTENT_EXPORT PowerSaveBlocker2 {
  public:
   enum PowerSaveBlockerType {
     // Prevent the application from being suspended. On some platforms, apps may
     // be suspended when they are not visible to the user. This type of block
     // requests that the app continue to run in that case, and on all platforms
     // prevents the system from sleeping.
     // Example use cases: downloading a file, playing audio.
     kPowerSaveBlockPreventAppSuspension,
 
     // Prevent the display from going to sleep. This also has the side effect of
     // preventing the system from sleeping, but does not necessarily prevent the
     // app from being suspended on some platforms if the user hides it.
     // Example use case: playing video.
     kPowerSaveBlockPreventDisplaySleep,
   };
 
   // Pass in the type of power save blocking desired. If multiple types of
   // blocking are desired, instantiate one PowerSaveBlocker for each type.
   // |reason| may be provided to the underlying system APIs on some platforms.
   PowerSaveBlocker2(PowerSaveBlockerType type, const std::string& reason);
   ~PowerSaveBlocker2();
 
  private:
   class Delegate;
 
   // Implementations of this class may need a second object with different
   // lifetime than the RAII container, or additional storage. This member is
   // here for that purpose. If not used, just define the class as an empty
-  // RefCounted like so to make it compile:
+  // RefCounted (or RefCountedThreadSafe) like so to make it compile:
   // class PowerSaveBlocker2::Delegate
-  //     : public RefCounted<PowerSaveBlocker2::Delegate> {
+  //     : public base::RefCounted<PowerSaveBlocker2::Delegate> {
+  //  private:
+  //   friend class base::RefCounted<Delegate>;
+  //   ~Delegate() {}
   // };
   scoped_refptr<Delegate> delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(PowerSaveBlocker2);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_POWER_SAVE_BLOCKER_H_