Add the navigation redirect-chain to Sync sessions proto for offline analysis.

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 dc3670d270398a3dcf63d96b27ff655041359ba6..bde8924858432fc6182c218c184420d5d7731fe0 100644
--- a/sync/protocol/session_specifics.proto
+++ b/sync/protocol/session_specifics.proto
@@ -134,9 +134,22 @@ message TabNavigation {
   repeated string content_pack_categories = 19;
   // 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.
   optional int32 referrer_policy = 21 [default = 1];
   // True if created from restored navigation entry that hasn't been loaded.
   optional bool is_restored = 22;
+  // The chain of redirections for this navigation, from the original URL
+  // through the last URL that redirected.
+  repeated NavigationRedirect navigation_redirect = 23;
+  // Normally not present.
+  // The last URL traversed when different from the virtual_url.
+  optional string last_navigation_redirect_url = 24;
+}
+
+// Navigation information for a single redirection within a single navigation.
+message NavigationRedirect {
+  // A URL that redirected while navigating to the virtual_url.
+  optional string url = 1;
 }