Only presubmit warn when spammy logging is being added/modified.

Only presubmit warn when spammy logging is being added/modified.

Sky has a bunch of printfs that are only used for efficient
local debugging. Don't presubmit warn when a file that contains
one of these is modified unless the patch actually modifies them.

Do this by changing the presubmit to only look at the "+"
lines in the diff (which is what ChangedContents returns).

R=eseidel@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/d77dcf8b243f9dd19df7ee0b6d5db3a1a1e30f34

[ojan, 2014-12-09 17:18:01]

ojan@chromium.org changed reviewers:
+ eseidel@chromium.org, esprehn@chromium.org, jamesr@chromium.org

[ojan, 2014-12-09 17:21:05]

Oh, now I see that the normal way to do this is use ChangedContents. I'll switch
to that.

[ojan, 2014-12-09 17:30:02]

OK. Ready for review.

[eseidel, 2014-12-09 18:46:36]

I think we can test presubmits.  Last I knew there was a PRESUBMIT_test.py. 
Hard to tell if this works or not from reading, but lgtm.

[ojan, 2014-12-09 21:18:46]

Committed patchset #2 (id:20001) manually as
d77dcf8b243f9dd19df7ee0b6d5db3a1a1e30f34 (presubmit successful).