Fix integer cast warnings for cast_unittest

Disable files that causes warnings for cast_unittest. Also fixed some
integer cast warnings.

R=justinlin@chromium.org

Review URL: https://codereview.chromium.org/25944002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226871 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226871