Create variations target that depends on base.

chrome/browser/metrics/proto/trials_seed.proto

Index: chrome/browser/metrics/proto/trials_seed.proto
===================================================================
--- chrome/browser/metrics/proto/trials_seed.proto	(revision 220309)
+++ chrome/browser/metrics/proto/trials_seed.proto	(working copy)
@@ -1,22 +0,0 @@
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-syntax = "proto2";
-
-option optimize_for = LITE_RUNTIME;
-
-package chrome_variations;
-
-import "study.proto";
-
-// The TrialsSeed is a protobuf response from the server that contains the list
-// of studies and a serial number to uniquely identify its contents. The
-// serial number allows the client to easily determine if the list of
-// experiments has changed from the previous TrialsSeed seen by the client.
-//
-// Next tag: 3
-message TrialsSeed {
-  optional string serial_number = 1;
-  repeated Study study = 2;
-}