MSan: introduce a GYP flag to control origin tracking.

base/base.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'includes': [
     '../build/win_precompile.gypi',
@@ skipping 988 matching lines @@
           'dependencies!': [
             '../third_party/libc++/libc++.gyp:libcxx_proxy',
           ],
         }],
         ['tsan==1', {
           'sources': [
             'debug/tsan_suppressions.cc',
           ],
         }],
       ],
-      'cflags!': [
-        '-fsanitize=address',
-        '-fsanitize=thread',
-        '-fsanitize=memory',
-        '-fsanitize-memory-track-origins',
+      'cflags/': [
+        ['exclude', '-fsanitize='],
+        ['exclude', '-fsanitize-'],
       ],
       'direct_dependent_settings': {
         'ldflags': [
           '-Wl,-u_sanitizer_options_link_helper',
         ],
       },
     },
   ],
   'conditions': [
     ['OS!="ios"', {
@@ skipping 475 matching lines @@
             'base_unittests.isolate',
           ],
           'sources': [
             'base_unittests.isolate',
           ],
         },
       ],
     }],
   ],
 }