Avatar syncing for supervised users

sync/protocol/managed_user_specifics.proto

Index: sync/protocol/managed_user_specifics.proto
diff --git a/sync/protocol/managed_user_specifics.proto b/sync/protocol/managed_user_specifics.proto
index 2a6f1b347a832fe42c774b2c58433145c578f402..6c8190808039190a2eadb5c271eed9dc7b110e11 100644
--- a/sync/protocol/managed_user_specifics.proto
+++ b/sync/protocol/managed_user_specifics.proto
@@ -25,4 +25,12 @@ message ManagedUserSpecifics {
   optional bool acknowledged = 3 [default = false];
   // Master key for managed user cryptohome.
   optional string master_key = 4;
+  // A string representing the index of the supervised user avatar on Chrome.
+  // It has the following format:
+  // "chrome-avatar-index:INDEX" where INDEX is an integer.
+  optional string chrome_avatar = 5;
+  // A string representing the index of the supervised user avatar on Chrome OS.
+  // It has the following format:
+  // "chromeos-avatar-index:INDEX" where INDEX is an integer.
+  optional string chromeos_avatar = 6;
 }