WebRTC: Update to new machines after a->b lab move.

masters/master.tryserver.webrtc/slaves.cfg

 # 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.
 
 slaves = [
   # Linux.
   {
     'master': 'WebRTCTryServer',
     'os': 'linux',
     'version': 'trusty',
@@ skipping 41 matching lines @@
   } for i in range(77, 79)
 ] + [
   {
     'master': 'WebRTCTryServer',
     'os': 'linux',
     'version': 'trusty',
     'bits': '64',
     'builder': [
       'android_arm64_rel',
     ],
-    'hostname': 'build204-a4',
+    'hostname': 'build140-b4',
   },
   {
     'master': 'WebRTCTryServer',
     'os': 'linux',
     'version': 'trusty',
     'bits': '64',
     'builder': [
       'android_n6',
     ],
     'hostname': 'build39-b4',
@@ skipping 13 matching lines @@
   # Linux bare-metal machines with audio devices and headsets.
   {
     'master': 'WebRTCTryServer',
     'os': 'linux',
     'version': 'trusty',
     'bits': '64',
     'builder': [
       'linux_baremetal',
     ],
     'hostname': hostname,
-  } for hostname in ['build22-a4', 'build138-b4']
+  } for hostname in ['build144-b4', 'build138-b4']
 ] + [
   # Mac.
   {
     'master': 'WebRTCTryServer',
     'os': 'mac',
     'version': '10.10',
     'bits': '64',
     'builder': [
       'mac_asan',
       'mac_compile_dbg',
@@ skipping 61 matching lines @@
   # Windows bare-metal machines with audio devices and headsets.
   {
     'master': 'WebRTCTryServer',
     'os': 'win',
     'version': 'win7',
     'bits': '64',
     'builder': [
       'win_baremetal',
     ],
     'hostname': hostname,
-  } for hostname in ['build23-a4', 'build139-b4']
+  } for hostname in ['build143-b4', 'build139-b4']
 ]