Use -fstack-protector in Mac Debug builds.

We used to have this in debug.xcconfig, but it seems to have gotten lost when
we migrated to GYP.

BUG=16713 (not really, that's for release builds, but close enough)
TEST=none
Review URL: http://codereview.chromium.org/292036

git-svn-id: http://src.chromium.org/svn/trunk/src/build@29591 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -354,7 +354,11 @@
         'xcode_settings': {
           'COPY_PHASE_STRIP': 'NO',
           'GCC_OPTIMIZATION_LEVEL': '<(mac_debug_optimization)',
-          'OTHER_CFLAGS': [ '<@(debug_extra_cflags)', ],
+          'OTHER_CFLAGS': [
+            '-fstack-protector',
+            '-fstack-protector-all',
+            '<@(debug_extra_cflags)',
+          ],
         },
         'conditions': [
           [ 'OS=="win"', {