fix for index operation unparses

lib/compiler/implementation/tree/unparser.dart

Index: lib/compiler/implementation/tree/unparser.dart
diff --git a/lib/compiler/implementation/tree/unparser.dart b/lib/compiler/implementation/tree/unparser.dart
index 05b24260254451bb67f314f740ba13b5e4956b95..2a891eb8d6cbafcebf8c68e23f22743490475e69 100644
--- a/lib/compiler/implementation/tree/unparser.dart
+++ b/lib/compiler/implementation/tree/unparser.dart
@@ -179,7 +179,6 @@ class Unparser implements Visitor {
     if (node.endToken !== null) add(node.endToken.value);
   }
 
-
   unparseSendPart(Send node) {
     if (node.isPrefix) {
       visit(node.selector);
@@ -198,10 +197,29 @@ class Unparser implements Visitor {
     visit(node.argumentsNode);
   }
 
-  visitSendSet(SendSet node) {
-    unparseSendPart(node);
+  // Special case for assignments like "list[0] = 1".
+  visitListIndexSet(SendSet node) {
+    visit(node.receiver);
+    sb.add('[');
+    sb.add(node.arguments.head);
+    sb.add(']');
     add(node.assignmentOperator.token.value);
-    visit(node.argumentsNode);
+    NodeList tailArguments = new NodeList(
+        node.argumentsNode.beginToken, node.argumentsNode.nodes.tail, node.argumentsNode.endToken,
+        node.argumentsNode.delimiter);
+    visit(tailArguments);
+  }
+
+  visitSendSet(SendSet node) {
+    Operator op = node.selector.asOperator();
+    bool isListIndex = op !== null && op.source.stringValue == '[]';

[Anton Muhin, 2012/05/24 16:59:58]

I believe we have exactly the same problem for expressions like l[0], e.g. var x
= l[0].  So solution should be in unparseSendPart

+    if (isListIndex) {
+      visitListIndexSet(node);
+    } else {
+      unparseSendPart(node);
+      add(node.assignmentOperator.token.value);
+      visit(node.argumentsNode);
+    }
   }
 
   visitThrow(Throw node) {