[tools] Fix callstats.py to correctly bucket OptimizeBackground events

This cl: https://chromium-review.googlesource.com/c/v8/v8/+/1924439 has
renamed the optimize passed happening on the backgroudn to
OptimizeBackground instead of OptimizeConcurrent or RecompileConcurrent.
Concurrent optimization has main thread phases so using
OptimizeConcurrent for background computations only was a bit confusing.

Bug: chromium:1029456
Change-Id: Idd0a0ff82597bb18c2d8896c7288f268e59acc05
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1943156
Commit-Queue: Mythri Alle <mythria@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Auto-Submit: Mythri Alle <mythria@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65261}

tools/callstats.py

@@ -370,8 +370,7 @@ def read_stats(path, domain, args):
   if args.aggregate:
     groups = [
         ('Group-IC', re.compile(".*IC_.*")),
-        ('Group-OptimizeBackground',
-         re.compile(".*OptimizeConcurrent.*|RecompileConcurrent.*")),
+        ('Group-OptimizeBackground', re.compile(".*OptimizeBackground.*")),
         ('Group-Optimize',
          re.compile("StackGuard|.*Optimize.*|.*Deoptimize.*|Recompile.*")),
         ('Group-CompileBackground', re.compile("(.*CompileBackground.*)")),