Installer: remove uses of PlatformFile

BUG=322664
R=grt@chromium.org

Review URL: https://codereview.chromium.org/173853004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253168 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253168