Move referrer policy to a different field when serializing.

sync/protocol/session_specifics.proto

Index: sync/protocol/session_specifics.proto
diff --git a/sync/protocol/session_specifics.proto b/sync/protocol/session_specifics.proto
index bde8924858432fc6182c218c184420d5d7731fe0..d3518e67df705618328b61829434923c7f30b56f 100644
--- a/sync/protocol/session_specifics.proto
+++ b/sync/protocol/session_specifics.proto
@@ -135,8 +135,7 @@ message TabNavigation {
   // The status code from the last navigation.
   optional int32 http_status_code = 20;
 
-  // Referrer policy. Valid enums are defined in
-  // third_party/WebKit/public/platform/WebReferrerPolicy.h.
+  // Referrer policy. Old, broken value.
   optional int32 referrer_policy = 21 [default = 1];
   // True if created from restored navigation entry that hasn't been loaded.
   optional bool is_restored = 22;
@@ -146,6 +145,9 @@ message TabNavigation {
   // Normally not present.
   // The last URL traversed when different from the virtual_url.
   optional string last_navigation_redirect_url = 24;
+  // Correct referrer policy. Valid enums are defined in
+  // third_party/WebKit/public/platform/WebReferrerPolicy.h.
+  optional int32 correct_referrer_policy = 25 [default = 1];
 }
 
 // Navigation information for a single redirection within a single navigation.