Runtime errors will be suppressed in --rebaseline mode, unless the
--verbose flag is passed.

The reasoning behind (rebaseline && !verbose) and not just (verbose)
is to suppress harmless noise while updating the expectation for
existing, known good snippets, without hiding actually relevant
errors when the tool is used to write new expectation files.

In fact, some tests are supposed to produce a runtime error, which
might nevertheless alarm a developer who is just --rebaseline'ing.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1742723003

Cr-Commit-Position: refs/heads/master@{#34385}