Fixes bug in test-gap-resolver.cc that didn't test different move reps.
Fixes test canonicalization so all slots have the same type (non-float).
Improve test failure text output.

LOG=N
BUG=v8:5187

Review-Url: https://codereview.chromium.org/2169493002
Cr-Commit-Position: refs/heads/master@{#37915}