Generate tear-off closures dynamically.

dart/sdk/lib/_internal/compiler/implementation/js_emitter/metadata_emitter.dart

Index: dart/sdk/lib/_internal/compiler/implementation/js_emitter/metadata_emitter.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/js_emitter/metadata_emitter.dart b/dart/sdk/lib/_internal/compiler/implementation/js_emitter/metadata_emitter.dart
index f4597f3b9946389ee7dedb5a424331c19a09c13a..bfad81636c955b36660503dece89356eba4aeba7 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/js_emitter/metadata_emitter.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/js_emitter/metadata_emitter.dart
@@ -42,9 +42,9 @@ class MetadataEmitter extends CodeEmitterHelper {
     });
   }
 
-  jsAst.Node reifyDefaultArguments(FunctionElement function) {
+  List<int> reifyDefaultArguments(FunctionElement function) {
     FunctionSignature signature = function.computeSignature(compiler);
-    if (signature.optionalParameterCount == 0) return null;
+    if (signature.optionalParameterCount == 0) return const [];
     List<int> defaultValues = <int>[];
     for (Element element in signature.orderedOptionalParameters) {
       Constant value =
@@ -55,7 +55,7 @@ class MetadataEmitter extends CodeEmitterHelper {
               .getText();
       defaultValues.add(addGlobalMetadata(stringRepresentation));
     }
-    return js.toExpression(defaultValues);
+    return defaultValues;
   }
 
   int reifyMetadata(MetadataAnnotation annotation) {
@@ -113,9 +113,17 @@ class MetadataEmitter extends CodeEmitterHelper {
     buffer.write('];$n');
   }
 
+  // TODO(ahe): Delete this method.
   jsAst.Fun extendWithMetadata(FunctionElement element, jsAst.Fun code) {
     if (!backend.retainMetadataOf(element)) return code;
+    List<int> metadata = computeMetadata(element);
+    code.body.statements.add(js.string(metadata.join(',')).toStatement());
+    return code;
+  }
+
+  List<int> computeMetadata(FunctionElement element) {
     return compiler.withCurrentElement(element, () {
+      if (!backend.retainMetadataOf(element)) return const <int>[];
       List<int> metadata = <int>[];
       FunctionSignature signature = element.functionSignature;
       if (element.isConstructor()) {
@@ -135,8 +143,7 @@ class MetadataEmitter extends CodeEmitterHelper {
           metadata.add(reifyMetadata(link.head));
         }
       }
-      code.body.statements.add(js.string(metadata.join(',')).toStatement());
-      return code;
+      return metadata;
     });
   }
 }