update fasta scanner to always generate INDEX or INDEX_EQ tokens

pkg/compiler/lib/src/tree/unparser.dart

Index: pkg/compiler/lib/src/tree/unparser.dart
diff --git a/pkg/compiler/lib/src/tree/unparser.dart b/pkg/compiler/lib/src/tree/unparser.dart
index 0413e23263c73f5fc5e6c4d2e20a8b19479f7091..c258821a7d49a8c6acde6163a2ef788add68213d 100644
--- a/pkg/compiler/lib/src/tree/unparser.dart
+++ b/pkg/compiler/lib/src/tree/unparser.dart
@@ -386,7 +386,10 @@ class Unparser extends Indentation implements Visitor {
     if (node.nodes != null) {
       unparseNodeListFrom(node, node.nodes, spaces: spaces);
     }
-    if (node.endToken != null) write(node.endToken.value);
+    // if "[]" then beginToken == endToken ... only write beginToken

[ahe, 2017/03/09 12:45:18]

Change this comment to be a complete sentence. In particular, start with an
uppercase letter and end with a period.

[danrubel, 2017/03/13 14:56:44]

Done.
https://codereview.chromium.org/2747683003

+    if (node.endToken != null && node.endToken != node.beginToken) {
+      write(node.endToken.value);
+    }
   }
 
   visitNodeList(NodeList node) {