Base: Copy platform_file.* to files/file.*

This is just copying some files without adding them to any gyp
file. It looks like there is no value for git similarity that can
make https://codereview.chromium.org/82963004/ figure out where all
code comes from, so this CL is meant to provide the proper baseline.

BUG=322664
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/93413002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237654 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237654