Added extensions sync-related constants, switches, and clauses.

chrome/browser/sync/syncable/model_type.cc

Index: chrome/browser/sync/syncable/model_type.cc
diff --git a/chrome/browser/sync/syncable/model_type.cc b/chrome/browser/sync/syncable/model_type.cc
index dd3af20a890b665c7f3584f79217cca951f3e155..48780d0549d28dc2c04a11df0a179ddf3caa7542 100644
--- a/chrome/browser/sync/syncable/model_type.cc
+++ b/chrome/browser/sync/syncable/model_type.cc
@@ -7,6 +7,7 @@
 #include "chrome/browser/sync/engine/syncproto.h"
 #include "chrome/browser/sync/protocol/autofill_specifics.pb.h"
 #include "chrome/browser/sync/protocol/bookmark_specifics.pb.h"
+#include "chrome/browser/sync/protocol/extension_specifics.pb.h"
 #include "chrome/browser/sync/protocol/password_specifics.pb.h"
 #include "chrome/browser/sync/protocol/preference_specifics.pb.h"
 #include "chrome/browser/sync/protocol/sync.pb.h"
@@ -36,6 +37,9 @@ void AddDefaultExtensionValue(syncable::ModelType datatype,
     case TYPED_URLS:
       specifics->MutableExtension(sync_pb::typed_url);
       break;
+    case EXTENSIONS:
+      specifics->MutableExtension(sync_pb::extension);
+      break;
     default:
       NOTREACHED() << "No known extension for model type.";
   }
@@ -91,6 +95,9 @@ ModelType GetModelTypeFromSpecifics(const sync_pb::EntitySpecifics& specifics) {
   if (specifics.HasExtension(sync_pb::typed_url))
     return TYPED_URLS;
 
+  if (specifics.HasExtension(sync_pb::extension))
+    return EXTENSIONS;
+
   return UNSPECIFIED;
 }