docs(benchpress): reword a comment (#42096)

* this is a follow up on pr #42085 to change
  the wording of the comment explaining the fix.

PR Close #42096

packages/benchpress/src/metric/perflog_metric.ts

@@ -243,11 +243,12 @@ export class PerflogMetric extends Metric {
       // testing (this is triggered by us calling #timeBegin and #timeEnd).
       //
       // Previously, this was done by checking that the event name matched our mark name and that
-      // the phase was either "B" or "E" ("begin" or "end"). However, for some reason now this is
+      // the phase was either "B" or "E" ("begin" or "end"). However, since Chrome v90 this is
       // showing up as "-bpstart" and "-bpend" ("benchpress start/end"), which is what one would
       // actually expect since that is the mark name used in ChromeDriverExtension - see the
-      // #timeBegin and #timeEnd implementations in chrome_driver_extension.ts. We are not sure why
-      // the markName didn't show up with the "-bp(start/end)" suffix before.
+      // #timeBegin and #timeEnd implementations in chrome_driver_extension.ts. For
+      // backwards-compatibility with Chrome v89 (and older), we do both checks: the phase-based
+      // one ("B" or "E") and event name-based (the "-bp(start/end)" suffix).
       const isStartEvent = (ph === 'B' && name === markName) || name === markName + '-bpstart';
       const isEndEvent = (ph === 'E' && name === markName) || name === markName + '-bpend';
       if (isStartEvent) {