Sync defines with the GYP build.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
@@ skipping 318 matching lines @@
       ]
     }
 
     # Omit unwind support in official builds to save space. We can use breakpad
     # for these builds.
     if (is_chrome_branded && is_official_build) {
       cflags += [
         "-fno-unwind-tables",
         "-fno-asynchronous-unwind-tables",
       ]
+      defines += [ "NO_UNWIND_TABLES" ]
     } else {
       cflags += [ "-funwind-tables" ]
     }
   }
 
   # Linux/Android common flags setup.
   # ---------------------------------
   if (is_linux || is_android) {
     cflags += [
       "-fPIC",
@@ skipping 280 matching lines @@
       # http://code.google.com/p/chromium/issues/detail?id=90453
       "-Wsign-compare",
     ]
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.
     defines = [
       "__STDC_CONSTANT_MACROS",
       "__STDC_FORMAT_MACROS",
     ]
+
+    if (using_sanitizer) {
+      # _FORTIFY_SOURCE isn't really supported by Clang now, see
+      # http://llvm.org/bugs/show_bug.cgi?id=16821.
+      # It seems to work fine with Ubuntu 12 headers though, so use it in
+      # official builds.
+      #
+      # Non-chromium code is not guaranteed to compile cleanly with
+      # _FORTIFY_SOURCE. Also, fortified build may fail when optimizations are
+      # disabled, so only do that for Release build.
+      defines += [ "_FORTIFY_SOURCE=2" ]
+    }
   }
 }
 config("no_chromium_code") {
   cflags = []
   cflags_cc = []
   defines = []
 
   if (is_win) {
     cflags += [
       "/W3",  # Warning level 3.
@@ skipping 438 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }