New, simpler and faster line splitter.

New, simpler and faster line splitter.

Instead of dynamic programming and memoization, this uses a more
straightforward search space exploration. It avoids the combinatorial
explosion by only trying splits inside long lines.

Performance is noticeably better across the board. It slightly
regresses on very nasty lines that do not end up fitting. In
return for that, it produces optimal output (i.e. without
pre-emption bugs) in many more cases, and faster output in cases
where the old splitter would bog down.

It is also less code and easier to maintain.

Fix #360. Fix #380.

R=kevmoo@google.com

Committed: 05712e0e0400de95e0ba6f9729410b3401fbc320

[Bob Nystrom, 2015-07-23 16:13:22]

rnystrom@google.com changed reviewers:
+ kevmoo@google.com, pquitslund@google.com

[kevmoo, 2015-07-23 17:17:40]

lgtm

[Bob Nystrom, 2015-07-23 17:44:50]

Committed patchset #2 (id:20001) manually as
05712e0e0400de95e0ba6f9729410b3401fbc320 (presubmit successful).