dart2js: run dartfmt on tests

tests/compiler/dart2js/mirror_tree_shaking_test.dart

Index: tests/compiler/dart2js/mirror_tree_shaking_test.dart
diff --git a/tests/compiler/dart2js/mirror_tree_shaking_test.dart b/tests/compiler/dart2js/mirror_tree_shaking_test.dart
index 34f2b69943b7d3914a13047e13fd7aa7c94b205b..3618c816fdac8301a9ea64f7da01e18b7b1454a2 100644
--- a/tests/compiler/dart2js/mirror_tree_shaking_test.dart
+++ b/tests/compiler/dart2js/mirror_tree_shaking_test.dart
@@ -6,8 +6,7 @@
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/compiler.dart';
-import 'package:compiler/src/js_backend/js_backend.dart'
-       show JavaScriptBackend;
+import 'package:compiler/src/js_backend/js_backend.dart' show JavaScriptBackend;
 import 'package:expect/expect.dart';
 import 'memory_compiler.dart';
 
@@ -15,7 +14,7 @@ main() {
   DiagnosticCollector collector = new DiagnosticCollector();
   asyncTest(() async {
     CompilationResult result = await runCompiler(
-      memorySourceFiles: MEMORY_SOURCE_FILES, diagnosticHandler: collector);
+        memorySourceFiles: MEMORY_SOURCE_FILES, diagnosticHandler: collector);
     Compiler compiler = result.compiler;
     Expect.isTrue(collector.errors.isEmpty);
     Expect.isTrue(collector.infos.isEmpty);