Fix warnings in dart2js.

dart/lib/compiler/implementation/tree/prettyprint.dart

Index: dart/lib/compiler/implementation/tree/prettyprint.dart
diff --git a/dart/lib/compiler/implementation/tree/prettyprint.dart b/dart/lib/compiler/implementation/tree/prettyprint.dart
index 1755c01d5499121b3698a5c48504e669d587dd9d..d3ad21939e0643d2944438a4e99180d2a0bb243b 100644
--- a/dart/lib/compiler/implementation/tree/prettyprint.dart
+++ b/dart/lib/compiler/implementation/tree/prettyprint.dart
@@ -395,4 +395,72 @@ class PrettyPrinter implements Visitor {
   visitWhile(While node) {
     visitNodeWithChildren(node, "While");
   }
+
+  visitNode(Node node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitCombinator(Combinator node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitExport(Export node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitExpression(Expression node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitGotoStatement(GotoStatement node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitImport(Import node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitLibraryName(LibraryName node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitLibraryTag(LibraryTag node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitLiteral(Literal node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitLoop(Loop node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitPart(Part node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitPartOf(PartOf node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitPostfix(Postfix node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitPrefix(Prefix node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitStatement(Statement node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  visitStringNode(StringNode node) {
+    unimplemented('visitNode', node: node);
+  }
+
+  unimplemented(String message, {Node node}) {
+    throw message;
+  }
 }