Create variations target that depends on base.

components/variations/variations_associated_data.h

Index: components/variations/variations_associated_data.h
===================================================================
--- components/variations/variations_associated_data.h	(revision 0)
+++ components/variations/variations_associated_data.h	(working copy)
@@ -0,0 +1,155 @@
+// Copyright 2013 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 COMPONENTS_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_
+#define COMPONENTS_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_
+
+#include <map>
+#include <string>
+
+#include "base/metrics/field_trial.h"
+
+// This file provides various helpers that extend the functionality around
+// base::FieldTrial.
+//
+// This includes several simple APIs to handle getting and setting additional
+// data related to Chrome variations, such as parameters and Google variation
+// IDs. These APIs are meant to extend the base::FieldTrial APIs to offer extra
+// functionality that is not offered by the simpler base::FieldTrial APIs.
+//
+// The AssociateGoogleVariationID and AssociateVariationParams functions are
+// generally meant to be called by the VariationsService based on server-side
+// variation configs, but may also be used for client-only field trials by
+// invoking them directly after appending all the groups to a FieldTrial.
+//
+// Experiment code can then use the getter APIs to retrieve variation parameters
+// or IDs:
+//
+//  std::map<std::string, std::string> params;
+//  if (GetVariationParams("trial", &params)) {
+//    // use |params|
+//  }
+//
+//  std::string value = GetVariationParamValue("trial", "param_x");
+//  // use |value|, which will be "" if it does not exist
+//
+// VariationID id = GetGoogleVariationID(GOOGLE_WEB_PROPERTIES, "trial",
+//                                       "group1");
+// if (id != chrome_variations::kEmptyID) {
+//   // use |id|
+// }
+
+namespace chrome_variations {
+
+typedef int VariationID;
+
+const VariationID EMPTY_ID = 0;
+
+// The Unique ID of a trial and its active group, where the name and group
+// identifiers are hashes of the trial and group name strings.
+struct ActiveGroupId {
+  uint32 name;
+  uint32 group;
+};
+
+// Returns an ActiveGroupId struct for the given trial and group names.
+ActiveGroupId MakeActiveGroupId(const std::string& trial_name,
+                                const std::string& group_name);
+
+// We need to supply a Compare class for templates since ActiveGroupId is a
+// user-defined type.
+struct ActiveGroupIdCompare {
+  bool operator() (const ActiveGroupId& lhs, const ActiveGroupId& rhs) const {
+    // The group and name fields are just SHA-1 Hashes, so we just need to treat
+    // them as IDs and do a less-than comparison. We test group first, since
+    // name is more likely to collide.
+    if (lhs.group != rhs.group)
+      return lhs.group < rhs.group;
+    return lhs.name < rhs.name;
+  }
+};
+
+// A key into the Associate/Get methods for VariationIDs. This is used to create
+// separate ID associations for separate parties interested in VariationIDs.
+enum IDCollectionKey {
+  // This collection is used by Google web properties, transmitted through the
+  // X-Chrome-Variations header.
+  GOOGLE_WEB_PROPERTIES,
+  // This collection is used by Google update services, transmitted through the
+  // Google Update experiment labels.
+  GOOGLE_UPDATE_SERVICE,
+  // The total count of collections.
+  ID_COLLECTION_COUNT,
+};
+
+// Associate a chrome_variations::VariationID value with a FieldTrial group for
+// collection |key|. If an id was previously set for |trial_name| and
+// |group_name|, this does nothing. The group is denoted by |trial_name| and
+// |group_name|. This must be called whenever a FieldTrial is prepared (create
+// the trial and append groups) and needs to have a
+// chrome_variations::VariationID associated with it so Google servers can
+// recognize the FieldTrial. Thread safe.
+void AssociateGoogleVariationID(IDCollectionKey key,
+                                const std::string& trial_name,
+                                const std::string& group_name,
+                                VariationID id);
+
+// As above, but overwrites any previously set id. Thread safe.
+void AssociateGoogleVariationIDForce(IDCollectionKey key,
+                                     const std::string& trial_name,
+                                     const std::string& group_name,
+                                     VariationID id);
+
+// Retrieve the chrome_variations::VariationID associated with a FieldTrial
+// group for collection |key|. The group is denoted by |trial_name| and
+// |group_name|. This will return chrome_variations::kEmptyID if there is
+// currently no associated ID for the named group. This API can be nicely
+// combined with FieldTrial::GetActiveFieldTrialGroups() to enumerate the
+// variation IDs for all active FieldTrial groups. Thread safe.
+VariationID GetGoogleVariationID(IDCollectionKey key,
+                                 const std::string& trial_name,
+                                 const std::string& group_name);
+
+// Associates the specified set of key-value |params| with the variation
+// specified by |trial_name| and |group_name|. Fails and returns false if the
+// specified variation already has params associated with it or the field trial
+// is already active (group() has been called on it). Thread safe.
+bool AssociateVariationParams(const std::string& trial_name,
+                              const std::string& group_name,
+                              const std::map<std::string, std::string>& params);
+
+// Retrieves the set of key-value |params| for the variation associated with
+// the specified field trial, based on its selected group. If the field trial
+// does not exist or its selected group does not have any parameters associated
+// with it, returns false and does not modify |params|. Calling this function
+// will result in the field trial being marked as active if found (i.e. group()
+// will be called on it), if it wasn't already. Currently, this information is
+// only available from the browser process. Thread safe.
+bool GetVariationParams(const std::string& trial_name,
+                        std::map<std::string, std::string>* params);
+
+// Retrieves a specific parameter value corresponding to |param_name| for the
+// variation associated with the specified field trial, based on its selected
+// group. If the field trial does not exist or the specified parameter does not
+// exist, returns an empty string. Calling this function will result in the
+// field trial being marked as active if found (i.e. group() will be called on
+// it), if it wasn't already. Currently, this information is only available from
+// the browser process. Thread safe.
+std::string GetVariationParamValue(const std::string& trial_name,
+                                   const std::string& param_name);
+
+// Expose some functions for testing.
+namespace testing {
+
+// Clears all of the mapped associations.
+void ClearAllVariationIDs();
+
+// Clears all of the associated params.
+void ClearAllVariationParams();
+
+}  // namespace testing
+
+}  // namespace chrome_variations
+
+#endif  // COMPONENTS_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_