Support parsing of enums in dart2js.

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

Index: sdk/lib/_internal/compiler/implementation/tree/nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/tree/nodes.dart b/sdk/lib/_internal/compiler/implementation/tree/nodes.dart
index 5bb147e3b8d9ecf4beea419b4cc7539be7637bce..3ec51ac872906b71783b5f8f4429cf4e1924b411 100644
--- a/sdk/lib/_internal/compiler/implementation/tree/nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/tree/nodes.dart
@@ -21,6 +21,7 @@ abstract class Visitor<R> {
   R visitContinueStatement(ContinueStatement node) => visitGotoStatement(node);
   R visitDoWhile(DoWhile node) => visitLoop(node);
   R visitEmptyStatement(EmptyStatement node) => visitStatement(node);
+  R visitEnum(Enum node) => visitNode(node);
   R visitExport(Export node) => visitLibraryDependency(node);
   R visitExpression(Expression node) => visitNode(node);
   R visitExpressionStatement(ExpressionStatement node) => visitStatement(node);
@@ -153,6 +154,7 @@ abstract class Node extends NullTreeElementMixin implements Spannable {
   ContinueStatement asContinueStatement() => null;
   DoWhile asDoWhile() => null;
   EmptyStatement asEmptyStatement() => null;
+  Enum asEnum() => null;
   ErrorExpression asErrorExpression() => null;
   Export asExport() => null;
   Expression asExpression() => null;
@@ -1851,6 +1853,33 @@ class Import extends LibraryDependency {
 }
 
 /**
+ * An `enum` declaration.
+ *
+ * An `enum` defines a number of named constants inside a non-extensible class
+ */
+class Enum extends Node {
+  /** The name of the enum class. */
+  final Identifier name;
+  /** The names of the enum constants. */
+  final NodeList names;
+  final Token enumToken;
+
+  Enum(this.enumToken, this.name, this.names);
+
+  Enum asEnum() => this;
+
+  accept(Visitor visitor) => visitor.visitEnum(this);
+
+  visitChildren(Visitor visitor) {
+    name.accept(visitor);
+    if (names != null) names.accept(visitor);
+  }
+
+  Token getBeginToken() => enumToken;
+  Token getEndToken() => names.getEndToken();
+}
+
+/**
  * An [:export:] library tag.
  *
  * An export tag is dependency on another library where the exported identifiers