If you copy\paste a license header in such a way that \r\n line endings
are used (I have done this) then CheckLicense would fail. This is quite
confusing because the license looks perfect in most text editors. This
change tells CheckLicense to treat \r\n line endings as equivalent to \n
and let CheckForWindowsLineEndings do its job of warning about the \r\n
line endings. This avoids confusing presubmit messages.

Bug: 801033
Change-Id: I37fa4a6d9cd0f1a4dcce1267175f4b8fd298b906
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2951788Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>