Diagnose unbalanced parentheses better.

dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart

Index: dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart b/dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart
index a768b5038458be91960883793ce175f69e29d55d..573fc4f8dbc8a8ac8e9357c588cfbb3fb34380fc 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart
@@ -141,7 +141,15 @@ class Token implements Spannable {
   /**
    * The number of characters parsed by this token.
    */
-  int get slowCharCount => slowToString().length;
+  int get slowCharCount {
+    if (info == BAD_INPUT_INFO) {
+      // This is a token that wraps around an error message. Return 1
+      // instead of the size of the length of the error message.
+      return 1;
+    } else {
+      return slowToString().length;
+    }
+  }
 }
 
 /**