Added asynchronous notification of readiness to the StatisticsProvider, and

chrome/browser/chromeos/system/statistics_provider.h

 // Copyright (c) 2011 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 CHROME_BROWSER_CHROMEOS_SYSTEM_STATISTICS_PROVIDER_H_
 #define CHROME_BROWSER_CHROMEOS_SYSTEM_STATISTICS_PROVIDER_H_
 #pragma once
 
 #include <string>
 
+#include "base/callback.h"
+
 namespace chromeos {
 namespace system {
 
 // This interface provides access to Chrome OS statistics.
 class StatisticsProvider {
  public:
-  // Retrieve the named machine statistic (e.g. "hardware_class").
-  // This does not update the statistcs. If the |name| is not set, |result|
-  // preserves old value.
+  // Get the machine statistic with a key of |name| (e.g., "hardware_class").
+  // Returns true if the key was found, and data was returned in |result|.
+  // Returns false otherwise, and the contents of |result| are undefined.
+  // This call may block for an arbitrary length of time (waiting for statistics
+  // to load, or a timeout to take place).  If this function is called anytime
+  // after WhenReady() has invoked any callback, then this function is
+  // guaranteed not to block.
   virtual bool GetMachineStatistic(const std::string& name,
                                    std::string* result) = 0;
 
+  // Invokes |callback| on the UI loop once the statistics have been loaded.
+  // |callback| is immediately posted to the UI loop if the statistics are
+  // already available. All the statistics are available once |callback| is
+  // invoked, and GetMachineStatistic() can be invoked as many times as
+  // desired without blocking.
+  virtual void WhenReady(const base::Closure& callback) = 0;
+
   static StatisticsProvider* GetInstance();
 
  protected:
   virtual ~StatisticsProvider() {}
 };
 
 }  // namespace system
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SYSTEM_STATISTICS_PROVIDER_H_