Support serial number requests in variations service.

chrome/browser/metrics/variations_service.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 CHROME_BROWSER_METRICS_VARIATIONS_SERVICE_H_
 #define CHROME_BROWSER_METRICS_VARIATIONS_SERVICE_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
@@ skipping 22 matching lines @@
  public:
   VariationsService();
   virtual ~VariationsService();
 
   // Creates field trials based on Variations Seed loaded from local prefs. If
   // there is a problem loading the seed data, all trials specified by the seed
   // may not be created.
   bool CreateTrialsFromSeed(PrefService* local_prefs);
 
   // Calls FetchVariationsSeed once and repeats this periodically. See
-  // implementation for details on the period.
+  // implementation for details on the period. Must be called after
+  // |CreateTrialsFromSeed|.
   void StartRepeatedVariationsSeedFetch();
 
   // Starts the fetching process once, where |OnURLFetchComplete| is called with
   // the response.
   void FetchVariationsSeed();
 
   // net::URLFetcherDelegate implementation:
   virtual void OnURLFetchComplete(const net::URLFetcher* source) OVERRIDE;
 
   // Register Variations related prefs in Local State.
@@ skipping 66 matching lines @@
   void CreateTrialFromStudy(const Study& study,
                             const base::Time& reference_date);
 
   // Contains the current seed request. Will only have a value while a request
   // is pending, and will be reset by |OnURLFetchComplete|.
   scoped_ptr<net::URLFetcher> pending_seed_request_;
 
   // The URL to use for querying the variations server.
   GURL variations_server_url_;
 
+  // Cached serial number from the most recently fetched variations seed.
+  std::string variations_serial_number_;
+
+  // Tracks whether |CreateTrialsFromSeed| has been called, to ensure that
+  // it gets called prior to |StartRepeatedVariationsSeedFetch|.
+  bool create_trials_from_seed_called_;

[Ilya Sherman, 2012/08/02 23:40:49]

nit: This seems a little hacky.  Is there any way to more directly check whether
CreateTrialsFromSeed() initialized whatever data you're expecting to be
initialized?

[Alexei Svitkine (slow), 2012/08/02 23:51:02]

I can't think of a good way - the issue is that it's perfectly valid for
CreateTrialsFromSeed() to return early if there's no seed stored in prefs yet.

+
   // The timer used to repeatedly ping the server. Keep this as an instance
   // member so if VariationsService goes out of scope, the timer is
-  // automatically cancelled.
+  // automatically canceled.
   base::RepeatingTimer<VariationsService> timer_;
 };
 
 }  // namespace chrome_variations
 
 #endif  // CHROME_BROWSER_METRICS_VARIATIONS_SERVICE_H_