Reformat benchmarks/ with 3.8 style.

Change-Id: Ied900f7d85addabc586823139aa78b879be035ea
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/425182
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Reviewed-by: Lasse Nielsen <lrn@google.com>
Commit-Queue: Lasse Nielsen <lrn@google.com>

benchmarks/Utf8Decode/dart/Utf8Decode.dart

@@ -27,12 +27,11 @@ class Utf8Decode extends BenchmarkBase {
 
   static String _makeName(String language, int size, bool allowMalformed) {
     String name = 'Utf8Decode.$language.';
-    name +=
-        size >= 1000000
-            ? '${size ~/ 1000000}M'
-            : size >= 1000
-            ? '${size ~/ 1000}k'
-            : '$size';
+    name += size >= 1000000
+        ? '${size ~/ 1000000}M'
+        : size >= 1000
+        ? '${size ~/ 1000}k'
+        : '$size';
     if (allowMalformed) name += '.malformed';
     return name;
   }