Remove references to DrMemory from chromium repo.

third_party/re2/BUILD.gn

 # Copyright 2014 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.
 
 config("re2_config") {
   include_dirs = [ "src" ]
 }
 
 static_library("re2") {
   sources = [
@@ skipping 42 matching lines @@
     "src/util/strutil.cc",
     "src/util/utf.h",
     "src/util/util.h",
     "src/util/valgrind.cc",
     "src/util/valgrind.h",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   public_configs = [ ":re2_config" ]
-
-  # TODO(battre) If Dr. Memory is ever migrated to GN, a flag needs to be
-  # added for this that adds a MEMORY_SANITIZER define. See re2.gyp.
-  # if (is_drmemory) {
-  #   defines += [ "MEMORY_SANITIZER" ]
-  # }
 }