Add a mechanism to force parameters of a group to a specific value.

components/variations/variations_associated_data.h

Index: components/variations/variations_associated_data.h
diff --git a/components/variations/variations_associated_data.h b/components/variations/variations_associated_data.h
index 79f31a31e0516904de7f7a262a785d8742cdefdd..7aac5c9a913f90942f71d10f5ceb8ceeefcf3c26 100644
--- a/components/variations/variations_associated_data.h
+++ b/components/variations/variations_associated_data.h
@@ -113,6 +113,10 @@ bool AssociateVariationParams(const std::string& trial_name,
                               const std::string& group_name,
                               const std::map<std::string, std::string>& params);
 
+// TODO: describe string formating
+// TrialName1.GroupName1.Key1/Value1/TrialName2.GroupName2.Key2/Value2/

[Alexei Svitkine (slow), 2015/04/22 15:42:37]

How about trial.group.key/value/key/value,trial.group:k/v,k/v,

that way, we don't have to repeat trial/group names if there are a lot of params
for the same group.

[Alexei Svitkine (slow), 2015/04/24 16:17:26]

(Oops, realise above is inconsistent, meant
trial.group.key/value/key/value,trial.group:k/v/k/v,...

[danduong, 2015/04/24 16:22:08]

I'm still confused.

do you mean:
trial1.group1:k1/v1/k2/v2,trail2.group2:k1/v1/k2/v2/k3/v3,..

[Alexei Svitkine (slow), 2015/04/24 16:31:52]

Yes, sorry for not being very clear before.

+bool AssociateParamsFromString(const std::string&);
+
 // 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