Redo "Generate native class metadata as a JavaScript AST."

sdk/lib/_internal/compiler/implementation/js/nodes.dart

Index: sdk/lib/_internal/compiler/implementation/js/nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js/nodes.dart b/sdk/lib/_internal/compiler/implementation/js/nodes.dart
index 18139b29fd32709ad4cf4a49af5f6e378f4e878b..8e1256596fbdd346aaf30d83ad649a1186269d96 100644
--- a/sdk/lib/_internal/compiler/implementation/js/nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/js/nodes.dart
@@ -769,6 +769,9 @@ class ArrayInitializer extends Expression {
 
   ArrayInitializer(this.length, this.elements);
 
+  factory ArrayInitializer.from(List<Expression> expressions) =>
+      new ArrayInitializer(expressions.length, _convert(expressions));
+
   accept(NodeVisitor visitor) => visitor.visitArrayInitializer(this);
 
   void visitChildren(NodeVisitor visitor) {
@@ -776,6 +779,12 @@ class ArrayInitializer extends Expression {
   }
 
   int get precedenceLevel => PRIMARY;
+
+  static List<ArrayElement> _convert(List<Expression> expressions) {
+    int index = 0;
+    return expressions.map(
+        (expression) => new ArrayElement(index++, expression));
+  }
 }
 
 /**