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

This cl: https://chromium-review.googlesource.com/c/v8/v8/+/1924439 has
renamed the optimize passed happening on the background 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: I8f4a485831851d5a43ab87b3a5d74857559fd679
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1944157
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@{#65425}

tools/callstats.html

@@ -1719,7 +1719,7 @@ code is governed by a BSD-style license that can be found in the LICENSE file.
     Group.add('total', new Group('Total', /.*Total.*/, '#BBB'));
     Group.add('ic', new Group('IC', /.*IC_.*/, "#3366CC"));
     Group.add('optimize-background', new Group('Optimize-Background',
-        /(.*OptimizeConcurrent.*)|RecompileConcurrent.*/, "#702000"));
+        /(.*OptimizeBackground.*)/, "#702000"));
     Group.add('optimize', new Group('Optimize',
         /StackGuard|.*Optimize.*|.*Deoptimize.*|Recompile.*/, "#DC3912"));
     Group.add('compile-background', new Group('Compile-Background',