Add finch control of user population in low reputation requests

components/safe_browsing/csd.proto

Index: components/safe_browsing/csd.proto
diff --git a/components/safe_browsing/csd.proto b/components/safe_browsing/csd.proto
index a69cd10bba7179ee99e34a5f417b79702a255726..9c72551109932a12956c398a3da8c97d3eed2874 100644
--- a/components/safe_browsing/csd.proto
+++ b/components/safe_browsing/csd.proto
@@ -34,6 +34,14 @@ message ChromeUserPopulation {
     EXTENDED_REPORTING = 2;
   }
   optional UserPopulation user_population = 1;
+
+  // If user enabled history sync.
+  optional bool is_history_sync_enabled = 2;
+
+  // The finch active group this user belongs to (if any). Active group is

[Nathan Parker, 2017/05/05 20:58:22]

We should at some point list the possible values of this, or point to the
google3 finch config name that lists them. That way when people are dremeling,
they know what to look for.

[Jialiu Lin, 2017/05/05 22:19:32]

ChromeUserPopulation message is not only used by PhishGuard. I am concerned that
this list could potentially grow very long if we are going to list all the
possible trial experiment names here.  

+  // defined by finch trial name and group name. Trial name and group name are
+  // concatenated with separator "|", e.g. "PingOnlyTrial|DefaultGroup".
+  optional string finch_active_group = 3;

[Nathan Parker, 2017/05/05 20:58:22]

This seems useful, but then what is a concrete use case? And would it tell us if
a use is enabled for both pings or just how they got enabled for this ping?

[Jialiu Lin, 2017/05/05 22:19:32]

My current implementation does the later (how they got enabled for this ping).
Changed to a repeated field and report all the PhishGuard related trials this
user is in.

 }
 
 message ClientPhishingRequest {
@@ -214,6 +222,9 @@ message LoginReputationClientRequest {
 
   // The number of verdicts stored on the client.
   optional int32 stored_verdict_cnt = 5;
+
+  // Chrome user population.
+  optional ChromeUserPopulation population = 6;
 }
 
 // The message is used for client response for login reputation requests.