fix "may be used uninitialized" warnings for older compilers

This small change keeps some slightly older compilers happy (gcc 4.5).

Review URL: https://codereview.chromium.org/78863002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236769 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236769