Use more hardening flags:

build/common.gypi

 # 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 2235 matching lines @@
             'inherit_from': ['Common_Base', 'x64_Base', 'Debug_Base'],
           },
           'Release_x64': {
             'inherit_from': ['Common_Base', 'x64_Base', 'Release_Base'],
           },
         }],
       ],
     },
   },
   'conditions': [
+    ['os_posix==1', {
+      'target_defaults': {
+        'cflags': [
+          # TODO(phajdan.jr): Use -fstack-protector-strong when our gcc
+          # supports it.
+          '-fstack-protector',
+          '--param=ssp-buffer-size=4',
+        ],
+        'ldflags': [
+          '-Wl,-z,now',
+          '-Wl,-z,relro',
+        ],
+        'conditions': [
+          ['chromium_code==1', {
+            # Non-chromium code is not guaranteed to compile cleanly
+            # with _FORTIFY_SOURCE.
+            'defines': [
+              '_FORTIFY_SOURCE=2',
+            ],
+          }],
+        ],
+      },
+    }],
     ['os_posix==1 and OS!="mac" and OS!="ios"', {
       'target_defaults': {
         # Enable -Werror by default, but put it in a variable so it can
         # be disabled in ~/.gyp/include.gypi on the valgrind builders.
         'variables': {
           'werror%': '-Werror',
           'libraries_for_target%': '',
         },
         'defines': [
           '_FILE_OFFSET_BITS=64',
@@ skipping 1531 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }