Add a Variables pane to the SkSL debugger.

The currently-active stack frame is always shown. Values which were
modified during the last step action are highlighted.

http://screen/4E4BLXYJsDR5bhk

Change-Id: I521d92fa6c1eabd64aaeeb188c71f04a79f827f5
Bug: skia:12666
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/483602
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed