Introduce different repo types (git and gitiles)

recipe_engine/package.proto

-// NOTE: this must be kept in sync with
-// https://github.com/luci/luci-go/blob/master/client/cmd/kitchen/proto/package.proto
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+// Recompile with libprotoc 2.5.0:
+// protoc -I recipe_engine recipe_engine/package.proto --python_out=recipe_engine
+
 syntax = "proto2";
 
 package recipe_engine;
 
 message DepSpec {
   optional string project_id = 1;
   optional string url = 2;
   optional string branch = 3;
   optional string revision = 4;
 
   // Treat a subtree of a repo as a whole repo unto itself.
   optional string path_override = 5;
+
+  enum RepoType {
+    GIT = 0;
+    GITILES = 1;
+  }
+  optional RepoType repo_type = 6 [default = GIT];
 }
 
 message Package {
   optional int32 api_version = 1;  // Version 1
   optional string project_id = 2;
   optional string recipes_path = 3;
   repeated DepSpec deps = 4;
 }