Assume a zone is in scope instead of a handles object.
Move INT32_TYPE into test-typing-reset.
Provide a CHECK_SKIP() macro to allow skipping
sections of an ast expression walk.

BUG= https://code.google.com/p/v8/issues/detail?id=4203
TEST=test-typing-reset, test-ast-expression-visitor
R=rossberg@chromium.org,titzer@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1319983004

Cr-Commit-Position: refs/heads/master@{#30484}