Improve v8_benchmark expectations on mac 10.6 after v8 roll to 3.9.21

BUG=none
TBR=cmp
Review URL: https://chromiumcodereview.appspot.com/9809028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@128940 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed