Add depot_tools builder to infra waterfall.

masters/master.chromium.infra/slaves.cfg

 # -*- python -*-
 # ex: set syntax=python:
 
 # Copyright 2015 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.
 
 slaves = [
   {
     'master': 'Infra',
     'builder': [
       'conda-cipd-pkg-trusty-64',
       'infra-continuous-trusty-64',
       'luci-gae-trusty64',
       'luci-go-trusty64',
+      'depot_tools zip uploader',
     ],
     'hostname': 'vm822-m1',
     'os': 'linux',
     'version': 'trusty',
     'bits': '64',
   },
   {
     'master': 'Infra',
     'builder': ['infra-continuous-trusty-32'],
     'hostname': 'vm26-m1',
@@ skipping 90 matching lines @@
       'conda-cipd-pkg-win-64',
       'infra-continuous-win-64',
       'luci-go-win64',
     ],
     'hostname': 'vm412-m1',
     'os': 'win',
     'version': 'win7',
     'bits': '64',
   },
 ]