Adding some functions that operate on file handles.

TEST=platform_file_unittest.cc
BUG=none
TBR=darin

Review URL: http://codereview.chromium.org/3354020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@59041 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed