[Android] Fix ndk_next gn args in mb_config.

tools/mb/mb_config.pyl

 # 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.
 
 {
   # This is a map of buildbot master names -> buildbot builder names ->
   # config names (where each config name is a key in the 'configs' dict,
   # below). MB uses this dict to look up which config to use for a given bot.
   'masters': {
     'chromeos.chrome': {
@@ skipping 1720 matching lines @@
 
     'msan': {
       'gn_args': 'is_msan=true msan_track_origins=2 use_prebuilt_instrumented_libraries=true',
     },
 
     'msan_no_origins': {
       'gn_args': 'is_msan=true msan_track_origins=0 use_prebuilt_instrumented_libraries=true',
     },
 
     'ndk_next': {
-      'gn_args': 'android_ndk_version=r13b android_ndk_major_version=13',
+      'gn_args': 'android_ndk_version="r13b" android_ndk_major_version="13"',
     },
 
     'no_pch': {
       'gn_args': 'enable_precompiled_headers=false',
     },
 
     'no_symbols': {
       'gn_args': 'symbol_level=0',
     },
 
@@ skipping 108 matching lines @@
 
     'x64': {
       'gn_args': 'target_cpu="x64"',
     },
 
     'x86': {
       'gn_args': 'target_cpu="x86"',
     },
   },
 }