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>
 
 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.
+  class Observer {
+   public:
+    virtual ~Observer() {}
+
+    // Invoked on the UI thread once the statistics have been loaded.
+    // Any calls to GetMachineStatistic() after this callback are guaranteed
+    // not to block.
+    virtual void OnMachineStatisticsReady() = 0;
+  };
+
+  // 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 OnMachineStatisticsReady() has been invoked on an observer,
+  // then this function is guaranteed not to block.
   virtual bool GetMachineStatistic(const std::string& name,
                                    std::string* result) = 0;
 
+  // Invokes OnMachineStatisticsReady() on the |observer| once the machine
+  // statistics are ready. That call can be executed synchronously if the
+  // statistics are already ready.
+  virtual void AddObserver(Observer* observer) = 0;
+
+  // Removes the given |observer|. Observers must be removed before shutdown.
+  virtual void RemoveObserver(Observer* observer) = 0;
+
   static StatisticsProvider* GetInstance();
 
  protected:
   virtual ~StatisticsProvider() {}
 };
 
 }  // namespace system
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SYSTEM_STATISTICS_PROVIDER_H_