Create variations target that depends on base.

components/variations/proto/trials_seed.proto

 // 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;
 }