[Sync] Move sync/{internal_api,syncable} into syncer namespace

sync/syncable/syncable_id.h

Index: sync/syncable/syncable_id.h
diff --git a/sync/syncable/syncable_id.h b/sync/syncable/syncable_id.h
index bcc66f5233f790a4e99c32c74cb3a979cac45528..6c451ade691cfa3e887c2ad2156ba33fdab0625f 100644
--- a/sync/syncable/syncable_id.h
+++ b/sync/syncable/syncable_id.h
@@ -23,12 +23,10 @@ namespace sql {
 class Statement;
 }
 
+namespace syncer {
 namespace syncable {
 struct EntryKernel;
 class Id;
-}
-
-namespace syncable {
 
 std::ostream& operator<<(std::ostream& out, const Id& id);
 
@@ -127,5 +125,6 @@ class Id {
 Id GetNullId();
 
 }  // namespace syncable
+}  // namespace syncer
 
 #endif  // SYNC_SYNCABLE_SYNCABLE_ID_H_