This allows people writing code stubs to just verify the graph of the stub they're working on, at least until we fix all of the issues we have and enable the verification by default.

Also fixes representations in CodeStubAssembler::SmiOr and InterpreterAssembler::StarDispatchLookahead.

R=bmeurer@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2413653006
Cr-Commit-Position: refs/heads/master@{#40320}