[Mac] Fix the 10.6 SDK build that was broken by r115270.
[Mac] Fix the 10.6 SDK build that was broken by r115270.

BUG=none
TEST=Compile with mac_sdk=10.6

Review URL: http://codereview.chromium.org/9021023

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@115352 0039d316-1c4b-4281-b951-d872f2087c98

yitian134/chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,adobe/chromium,adobe/chromium,gavinp/chromium,adobe/chromium,ropik/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,adobe/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,ropik/chromium,ropik/chromium,ropik/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,gavinp/chromium,gavinp/chromium,ropik/chromium,yitian134/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,yitian134/chromium,yitian134/chromium,yitian134/chromium