Use ASTVisitor as in new AST.

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

Index: compiler/java/com/google/dart/compiler/ast/DartComment.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartComment.java b/compiler/java/com/google/dart/compiler/ast/DartComment.java
index 2f8cbae1253303f5b9a90b69b48872a93388b382..4e25c0492ed9fe56169a41aafcf1248bc420c904 100644
--- a/compiler/java/com/google/dart/compiler/ast/DartComment.java
+++ b/compiler/java/com/google/dart/compiler/ast/DartComment.java
@@ -49,15 +49,11 @@ public class DartComment extends DartNode {
   }
 
   @Override
-  public void traverse(DartVisitor v, DartContext ctx) {
+  public void visitChildren(ASTVisitor<?> visitor) {
   }
 
   @Override
-  public void visitChildren(DartPlainVisitor<?> visitor) {
-  }
-
-  @Override
-  public <R> R accept(DartPlainVisitor<R> visitor) {
+  public <R> R accept(ASTVisitor<R> visitor) {
     return null;
   }