Fix DAS completion benchmarks, after Flutter change.

After https://github.com/flutter/flutter/commit/73e1f23426c53c1593fc4a32e501027cb3c6ae35#diff-20c19d254b0a82027625f1246ba51cb2264bfabf105fe91d532c19e6a6d77478

Change-Id: Ibcb0327aa71c8d0d9bda3af71cbec582acbdbd9b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/308960
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
diff --git a/pkg/analysis_server/benchmark/perf/flutter_completion_benchmark.dart b/pkg/analysis_server/benchmark/perf/flutter_completion_benchmark.dart
index 7a6ea9a..e758fff 100644
--- a/pkg/analysis_server/benchmark/perf/flutter_completion_benchmark.dart
+++ b/pkg/analysis_server/benchmark/perf/flutter_completion_benchmark.dart
@@ -177,7 +177,7 @@
           await _completionTiming(
             test,
             filePath: '$flutterPkgPath/lib/src/material/app_bar.dart',
-            uniquePrefix: 'computeDryLayout(BoxConstraints',
+            uniquePrefix: '_handleScrollNotification(ScrollNotification',
             insertStringGenerator: _IncrementingStringGenerator().call,
             name: name,
           ),