Drive-by-fix 1: be more precise in machine representations for
AllocateNameDictionary to make --turbo_verify_machine_graph happy.

Drive-by-fix 2: Improve graph verifier output by printing input
representation.

BUG=

Review-Url: https://codereview.chromium.org/2475913002
Cr-Commit-Position: refs/heads/master@{#40797}