Make sure files end with exactly one new line and police this in presubmit.

The changes are (excluding presubmit.py) mechanical. I added the following
lines after the check and iterated the presubmit script until all errors
went away:

f = open(name, "w");
if contents.endswith('\n\n'):
  f.write(contents[0:-1])
else:
  f.write(contents + '\n')

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/82803005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18017 ce2b1a6d-e550-0410-aec6-3dcde31c8c00