ReadFile limits to reading files inside the repository.
CheckChangeHasNoCR reads the text files looking for \r and fails if found.

TEST=none
BUG=none

Review URL: http://codereview.chromium.org/118370

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@17857 0039d316-1c4b-4281-b951-d872f2087c98