Introduces a search term extraction mechanism working for arbitrary search providers.

sync/protocol/search_engine_specifics.proto

Index: sync/protocol/search_engine_specifics.proto
diff --git a/sync/protocol/search_engine_specifics.proto b/sync/protocol/search_engine_specifics.proto
index 037e9fa2cbc8f9ac9ced6bb7107dddbd4413133b..0857a512457ccd87d47124514fa6eeb730077f69 100644
--- a/sync/protocol/search_engine_specifics.proto
+++ b/sync/protocol/search_engine_specifics.proto
@@ -59,5 +59,8 @@ message SearchEngineSpecifics {
   optional int64 last_modified = 17;
   // The primary identifier of this search engine entry for Sync.
   optional string sync_guid = 18;
+  // A comma separated list of URL patterns that can be used, in addition to
+  // |url| and |instant_url|, to extract search terms from a URL.
+  optional string alternate_urls = 19;
 }