Disable the ASan SEGV handler for NaCl processes on Mac.

Implement __asan_default_options() for the Chrome OSX binary. This function
sets handle_segv=0 iff the binary is executed with --type=nacl-loader.

BUG=323510
TEST=browser_tests pass under ASan on OSX x64
R=cpu@chromium.org, mseaborn@chromium.org

Review URL: https://codereview.chromium.org/96683003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238328 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238328