In addition, remove the default branch from the swtich in HeapObjectPrint, so
that it's no longer possible to leave out printing functionality by accident.

BUG=v8:7308

Change-Id: I2db67549e328aea6228d3a370f9ebb7494ab3730
Reviewed-on: https://chromium-review.googlesource.com/997492
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52384}