Hide function return values after a step.

Previously, return values like `[func].result` would stick around in the
Variables table indefinitely. This felt very counterintuitive. Now they
only appear for one step, then vanish.

Change-Id: Iedfc7d2ddf136111005b26aaefb380ffc6281d05
Bug: skia:12666
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/483605
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
4 files changed