Support parameter metadata.

sdk/lib/_internal/compiler/implementation/tree/unparser.dart

Index: sdk/lib/_internal/compiler/implementation/tree/unparser.dart
diff --git a/sdk/lib/_internal/compiler/implementation/tree/unparser.dart b/sdk/lib/_internal/compiler/implementation/tree/unparser.dart
index 960c8b672d8e281cee9354235c572116758b5586..ebe86480bc8c372ee2263b29cc40794de10dadb0 100644
--- a/sdk/lib/_internal/compiler/implementation/tree/unparser.dart
+++ b/sdk/lib/_internal/compiler/implementation/tree/unparser.dart
@@ -359,6 +359,10 @@ class Unparser implements Visitor {
   }
 
   visitVariableDefinitions(VariableDefinitions node) {
+    if (node.metadata != null) {
+      visit(node.metadata);
+      sb.write(' ');
+    }
     visit(node.modifiers);
     if (!node.modifiers.nodes.isEmpty) {
       sb.write(' ');
@@ -573,6 +577,11 @@ class Unparser implements Visitor {
     visit(node.identifiers);
   }
 
+  visitMetadata(Metadata node) {
+    addToken(node.token);
+    visit(node.expression);
+  }
+
   visitNode(Node node) {
     throw 'internal error'; // Should not be called.
   }