Avoid reparsing metadata expressions

pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart

Index: pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
index bcc7977e3e670553270f27bc82353834e27090b5..b1e5bb213adfeab73eec83a7457b303a510e8d9b 100644
--- a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
@@ -665,12 +665,11 @@ class OldEmitter implements Emitter {
 
   void emitMetadata(Program program, CodeOutput output, OutputUnit outputUnit) {
 
-    jsAst.Expression constructList(List<String> list) {
-      String listAsString = list == null ? '[]' : '[${list.join(",")}]';
-      return js.uncachedExpressionTemplate(listAsString).instantiate([]);
+    jsAst.Expression constructList(List<jsAst.Expression> list) {
+      return new jsAst.ArrayInitializer(list == null ? [] : list);
     }
 
-    List<String> types = program.metadataTypes[outputUnit];
+    List<jsAst.Expression> types = program.metadataTypes[outputUnit];
 
     if (outputUnit == compiler.deferredLoadTask.mainOutputUnit) {
       jsAst.Expression metadataAccess =