Adjust TSR when migrating trailing newlines across zero-width nodes.

* This issue was found while investigating bug 63779. I noticed a
  "cs/s inconsistency warning" (which was off-by-1 char) and found that
  this was resulting in buggy DSR values.

* Eliminates four "cs/s inconsistency warnings" while running parser tests.

Bug: 63779
Change-Id: I437d577e65b020a30045900c11452c5f4803b8cc