Support duration events in `benchmark.mojo`.

apps/benchmark/run_args.cc

Index: apps/benchmark/run_args.cc
diff --git a/apps/benchmark/run_args.cc b/apps/benchmark/run_args.cc
index 6767c3e97de8a42913cf3a9b692aaef6c4230ea6..1791470bf8cd4baa692ce3b878f2701a89f4b50f 100644
--- a/apps/benchmark/run_args.cc
+++ b/apps/benchmark/run_args.cc
@@ -34,7 +34,7 @@ bool GetMeasurement(const std::string& measurement_spec, Measurement* result) {
     return false;
   }
 
-  result->target_event.category = parts[1];
+  result->target_event.categories = parts[1];
   result->target_event.name = parts[2];
   result->spec = measurement_spec;
   return true;