Change AccelerometerReader to a Singleton

chromeos/accelerometer/accelerometer_reader.h

 // Copyright 2014 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 CHROMEOS_ACCELEROMETER_ACCELEROMETER_READER_H_
 #define CHROMEOS_ACCELEROMETER_ACCELEROMETER_READER_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "chromeos/chromeos_export.h"
 #include "ui/accelerometer/accelerometer_types.h"
 
+template <typename T>
+struct DefaultSingletonTraits;
+
 namespace base {
 class TaskRunner;
 }
 
 namespace chromeos {
 
 // Reads an accelerometer device and reports data back to an
 // AccelerometerDelegate.
 class CHROMEOS_EXPORT AccelerometerReader {
  public:
@@ skipping 23 matching lines @@
   // An interface to receive data from the AccelerometerReader.
   class Observer {
    public:
     virtual void OnAccelerometerUpdated(
         const ui::AccelerometerUpdate& update) = 0;
 
    protected:
     virtual ~Observer() {}
   };
 
-  AccelerometerReader();
-  ~AccelerometerReader();
+  static AccelerometerReader* GetInstance();
 
   void Initialize(scoped_refptr<base::TaskRunner> blocking_task_runner);
 
   // Add/Remove observers.
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);
 
   // A reading is considered stable if its deviation from gravity is small. This
   // returns false if the deviation is too higher, or if |source| is not present
   // in the update.
   static bool IsReadingStable(const ui::AccelerometerUpdate& update,
                               ui::AccelerometerSource source);
 
+ protected:
+  AccelerometerReader();
+  virtual ~AccelerometerReader();
+
  private:
+  friend struct DefaultSingletonTraits<AccelerometerReader>;
+
   // Dispatched when initialization is complete. If |success|, |configuration|
   // provides the details of the detected accelerometer.
   void OnInitialized(scoped_refptr<Configuration> configuration, bool success);
 
   // Triggers an asynchronous read from the accelerometer, signalling
   // OnDataRead with the result.
   void TriggerRead();
 
   // If |success|, converts the raw reading to an AccelerometerUpdate
   // message and notifies the |delegate_| with the new readings.
@@ skipping 12 matching lines @@
   ObserverList<Observer, true> observers_;
 
   base::WeakPtrFactory<AccelerometerReader> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AccelerometerReader);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_ACCELEROMETER_ACCELEROMETER_READER_H_