Fixed temporary file management in pixel test on Windows.

BUG=330053
TBR=bajones@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/121853002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242629 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242629