We don't need/want to evict an inactive live range when it doesn't
overlap with the live range currently being considered.

This is especially important for Variables representing scratch
registers that are killed by call instructions.  These register
assignments should obviously never be evicted.

Note that the algorithm that computes the min-weight register to evict
doesn't consider inactive and non-overlapping live ranges.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3903
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/417933004