Better PrettyPrinter output for Return nodes, display tokens and expression.

lib/compiler/implementation/tree/prettyprint.dart

Index: lib/compiler/implementation/tree/prettyprint.dart
diff --git a/lib/compiler/implementation/tree/prettyprint.dart b/lib/compiler/implementation/tree/prettyprint.dart
index cb2eab34dd9f96c44c1cf77409481e67db438295..3baa3926c40c4aa288ce0929c25eacbb451eef9e 100644
--- a/lib/compiler/implementation/tree/prettyprint.dart
+++ b/lib/compiler/implementation/tree/prettyprint.dart
@@ -241,7 +241,12 @@ class PrettyPrinter implements Visitor {
   }
 
   visitReturn(Return node) {
-    visitNodeWithChildren(node, "Return");
+    var beginToken =
+        node.beginToken !== null ? node.beginToken.stringValue : "null";
+    var endToken = node.endToken !== null ? node.endToken.stringValue : "null";
+    openNode("Return", {"beginToken" : beginToken, "endToken" : endToken});
+    if (node.hasExpression) visitWithPrefix(node.expression, "expression:");
+    closeNode("Return");
   }
 
   visitScriptTag(ScriptTag node) {