Add support for metadata annotation syntax (issue 4056)

compiler/java/com/google/dart/compiler/ast/DartAnnotation.java

Index: compiler/java/com/google/dart/compiler/ast/DartAnnotation.java
===================================================================
--- compiler/java/com/google/dart/compiler/ast/DartAnnotation.java	(revision 0)
+++ compiler/java/com/google/dart/compiler/ast/DartAnnotation.java	(revision 0)
@@ -0,0 +1,52 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+package com.google.dart.compiler.ast;
+
+import java.util.List;
+
+
+/**
+ * Instances of the class {@code DartAnnotation} represent metadata that can be associated with an
+ * AST node.
+ * 
+ * <pre>
+ * metadata ::=
+ *     annotation*
+ * 
+ * annotation ::=
+ *     '@' qualified (‘.’ identifier)? arguments?
+ * </pre>
+ */
+public class DartAnnotation extends DartNode {
+  private DartExpression name;
+
+  private NodeList<DartExpression> arguments = NodeList.create(this);
+
+  public DartAnnotation(DartExpression name, List<DartExpression> arguments) {
+    this.name = becomeParentOf(name);
+    if (arguments != null) {
+      this.arguments.addAll(arguments);
+    }
+  }
+
+  @Override
+  public <R> R accept(ASTVisitor<R> visitor) {
+    return visitor.visitAnnotation(this);
+  }
+
+  public DartExpression getName() {
+    return name;
+  }
+
+  public NodeList<DartExpression> getArguments() {
+    return arguments;
+  }
+
+  @Override
+  public void visitChildren(ASTVisitor<?> visitor) {
+    safelyVisitChild(name, visitor);
+    arguments.accept(visitor);
+  }
+}