[dart2wasm] Use RunTimeRaw for metric printer in WasmDataTransfer benchmark

Golem config expects RunTimeRaw metric (as we want to see not runs per
second but a more meaningful benchmark, i.e. how much transferring 1KB
of data takes)

=> Golem cannot just display it in different form, we have to make the
    benchmark report it also as RunTimeRaw.
=> This CL should fix the golem benchmarks.

Change-Id: I91301930941986771eb0725fd0d85424bb07dc3a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/372640
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>

benchmarks/WasmDataTransfer/dart/WasmDataTransfer.dart

@@ -41,8 +41,17 @@ void main(List<String> args) {
   WasmDataTransferToBrowserBytes(largeDartBytes, '1MB').report();
 }
 
+class PrintEmitter implements ScoreEmitter {
+  const PrintEmitter();
+
+  @override
+  void emit(String testName, double value) {
+    print('$testName(RunTimeRaw): $value us.');
+  }
+}
+
 abstract class Benchmark extends BenchmarkBase {
-  Benchmark(super.name);
+  Benchmark(super.name) : super(emitter: const PrintEmitter());
 
   @override
   void exercise() {