Treat allocation of splintered ranges differently, by optimizing for move
counts (i.e. try to have less move counts), rather than optimizing for
quality of moves (which is what normal allocation does).

We can see reductions in code size in the benchmarks that measure it
(e.g. Unity)

BUG=

Review-Url: https://codereview.chromium.org/2347563004
Cr-Commit-Position: refs/heads/master@{#40178}