[mb] Add missing GN args for MSan

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 the list of configs that you can pass to mb; each config
   # represents a particular combination of GYP_DEFINES/gn args that
   # we must support. A given config *may* be platform-specific but
   # is not necessarily so (i.e., we might have mac, win, and linux
   # bots all using the 'gn_release_bot' config).
@@ skipping 298 matching lines @@
       'gn_args': 'symbol_level=1',
       'gyp_defines': 'fastbuild=1',
     },
 
     'mipsel': {
       'gn_args': 'target_cpu="mipsel"',
       'gyp_defines': 'target_arch=mipsel',
     },
 
     'msan': {
-      'gn_args': 'is_msan=true',
+      'gn_args': 'is_msan=true msan_track_origins=2 use_prebuilt_instrumented_libraries=true',
       'gyp_defines': 'msan=1 msan_track_origins=2 use_prebuilt_instrumented_libraries=1',
     },
 
     'no_symbols': {
       'gn_args': 'symbol_level=0',
       'gyp_defines': 'fastbuild=2',
     },
 
     'oilpan': {
       'gn_args': 'enable_oilpan=true',
@@ skipping 359 matching lines @@
       'win8_chromium_gn_upload': 'gn_release_bot_minimal_symbols_x86',
       'win_clang_x64_dbg': 'win_clang_debug_bot',
     },
     'tryserver.v8': {
       'v8_linux_chromium_gn_rel': 'gn_release_trybot',
       'v8_android_chromium_gn_dbg': 'android_gn_debug_bot',
       'v8_linux_blink_rel': 'swarming_gn_release_trybot_minimal_symbols_x64',
     },
   },
 }