X-Chrome-Variations logic refactoring

chrome/browser/chrome_metrics_helper.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_CHROME_METRICS_HELPER_H_
+#define CHROME_BROWSER_CHROME_METRICS_HELPER_H_
+
+#include <set>
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/metrics/field_trial.h"
+#include "base/synchronization/lock.h"
+#include "chrome/common/metrics/variations/variation_ids.h"
+
+namespace content {
+class ResourceContext;
+}
+
+namespace net {
+class HttpRequestHeaders;
+class URLFetcher;
+class URLRequest;
+}
+
+class GURL;
+class Profile;
+class ProfileIOData;
+
+template <typename T> struct DefaultSingletonTraits;
+
+// This class is a thread-safe singleton.

[SteveT, 2012/12/13 16:24:08]

Could you add a brief doc for this class?

[Bart N., 2012/12/14 18:21:42]

Done.

+class ChromeMetricsHelper : base::FieldTrialList::Observer {
+ public:
+  static ChromeMetricsHelper* GetInstance();
+
+  // Adds Chrome experiment and metrics state as custom headers to |request|.
+  // This is a best-effort attempt, and does not interrupt the request if the
+  // headers cannot be appended.
+  void AppendHeadersToRequest(net::URLRequest* request,
+                              content::ResourceContext* resource_context);
+  // Same as above but works with a |fetcher| and |profile|.  Both methods
+  // internally delegate to AppendHeaders(...).
+  void AppendHeadersToFetcher(net::URLFetcher* fetcher, const Profile* profile);
+
+ private:
+  friend struct DefaultSingletonTraits<ChromeMetricsHelper>;
+
+  ChromeMetricsHelper();
+  virtual ~ChromeMetricsHelper();
+
+  // base::FieldTrialList::Observer implementation.
+  // This will add the variation ID associated with |trial_name| and
+  // |group_name| to the variation ID cache.
+  virtual void OnFieldTrialGroupFinalized(
+      const std::string& trial_name,
+      const std::string& group_name) OVERRIDE;
+
+  // Adds Chrome experiment and metrics state as custom headers to |headers|.
+  // Some headers may not be set given the |incognito| mode or whether
+  // the user has |uma_enabled|.  Also, we never transmit headers to non-Google
+  // sites, which is checked based on the destination |url|.
+  void AppendHeaders(const GURL& url,
+                     bool incognito,
+                     bool uma_enabled,
+                     net::HttpRequestHeaders* headers);
+
+  // Prepares the variation IDs cache with initial values if not already done.
+  // This method also registers the caller with the FieldTrialList to receive
+  // new variation IDs.
+  void InitVariationIDsCacheIfNeeded();
+
+  // Takes whatever is currently in |variation_ids_set_| and recreates
+  // |variation_ids_header_| with it.
+  void UpdateVariationIDsHeaderValue();
+
+  // Guards |variation_ids_cache_initialized_|, |variation_ids_set_| and
+  // |variation_ids_header_|.
+  base::Lock lock_;
+
+  // Whether or not we've initialized the cache.
+  bool variation_ids_cache_initialized_;
+
+  // Keep a cache of variation IDs that are transmitted in headers to Google.
+  // This consists of a list of valid IDs, and the actual transmitted header.
+  std::set<chrome_variations::VariationID> variation_ids_set_;
+  std::string variation_ids_header_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChromeMetricsHelper);
+};
+
+#endif  // CHROME_BROWSER_CHROME_METRICS_HELPER_H_