Modify rappor parameters.

components/rappor/rappor_pref_names.cc

Index: components/rappor/rappor_pref_names.cc
diff --git a/components/rappor/rappor_pref_names.cc b/components/rappor/rappor_pref_names.cc
index e62c764cf86d739ee3c317c90e45236dbfc1d89c..74c857ad1fe6832a4bd9f68a494c5547ab368d35 100644
--- a/components/rappor/rappor_pref_names.cc
+++ b/components/rappor/rappor_pref_names.cc
@@ -7,8 +7,8 @@
 namespace rappor {
 namespace prefs {
 
-// A randomly generated number, which determines cohort data is reported for.
-const char kRapporCohort[] = "rappor.cohort";

[Alexei Svitkine (slow), 2014/05/20 06:59:49]

Keep the old pref and add code to Clear it, so that clients' prefs won't be
littered with old prefs. Then, after a few releases, remove code related to it.

[Steven Holte, 2014/05/20 18:28:03]

Is there a reliable pattern for doing a one time Clear of data, so that I can
ensure this only gets re-rolled once?

[Alexei Svitkine (slow), 2014/05/21 09:13:37]

Renaming the pref key the correct way to do this, but also keeping an entry for
the old name, i.e.:

const char kRapporCohortSeed[] = "rappor.cohort_seed";
// comment about it:
const char kRapporCohortDeprecated[] = "rappor.cohort";

And in your code that reads the new pref also clear the old pref.

See also metrics_state_manager.cc which does this for some prefs (e.g.
kMetricsOldLowEntropySource).

[Steven Holte, 2014/05/21 19:02:57]

Done. PTAL.

+// A randomly generated number, which determines cohorts data is reported for.
+const char kRapporCohortSeed[] = "rappor.cohort_seed";
 
 // A base-64 encoded, randomly generated byte string, which is used as a seed
 // for redacting collected data.