Add breakpoint support in SkSL debugger.

Line numbers were previously Text. They are now SmallButtons; clicking
them sets and clears breakpoints. The set of active breakpoints is
stored in an unordered_set of line numbers. Breakpoints are visualized
by setting the color of the SmallButton controls to red.

We now also have "Reset" (start over) and "Run to Breakpoint" buttons.

http://screen/8rtenW2vszxDgCp

Change-Id: I30a79bb09811e1d8a4e4e8535cbe62020f20f111
Bug: skia:12747
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/485861
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
3 files changed