In particular, don't clear environment for StackCheck.
Clear it for all throw and generator-related operations.

Also improve some printing.

Bug: v8:7790
Change-Id: I45d0994a06ba7ca430e78d631d85b2c6b2e9e323
Reviewed-on: https://chromium-review.googlesource.com/c/1439376
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59157}