[Buildfix] Fix PlatformFileInfo usage in pdf_browsertest.cc

BUG=None
TBR=thestig@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/125973003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243291 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243291