Enable side-by-side beta and dev channels.

chrome/install_static/google_chrome_install_modes.h

 // Copyright 2016 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.
 
 // Brand-specific types and constants for Google Chrome.
 
 #ifndef CHROME_INSTALL_STATIC_GOOGLE_CHROME_INSTALL_MODES_H_
 #define CHROME_INSTALL_STATIC_GOOGLE_CHROME_INSTALL_MODES_H_
 
 namespace install_static {
 
 enum : bool {
   kUseGoogleUpdateIntegration = true,
 };
 
 // Note: This list of indices must be kept in sync with the brand-specific
 // resource strings in chrome/installer/util/prebuild/create_string_rc.
 enum InstallConstantIndex {
   STABLE_INDEX,
+  BETA_INDEX,
+  DEV_INDEX,
   CANARY_INDEX,
   NUM_INSTALL_MODES,
 };
 
 }  // namespace install_static
 
 #endif  // CHROME_INSTALL_STATIC_GOOGLE_CHROME_INSTALL_MODES_H_