add previous token field

pkg/front_end/lib/src/fasta/scanner/token.dart

Index: pkg/front_end/lib/src/fasta/scanner/token.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/token.dart b/pkg/front_end/lib/src/fasta/scanner/token.dart
index 0c29f1c6ad0baadb7181d53042fa36e4634611a8..fff1f3cc54be1545bf04024e0315e9b53914ab6f 100644
--- a/pkg/front_end/lib/src/fasta/scanner/token.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/token.dart
@@ -29,6 +29,13 @@ abstract class Token {
   Token next;
 
   /**
+   * The previous token in the token stream.
+   * @deprecated This exists for compatibility with the Analyzer token stream

[Paul Berry, 2017/03/07 13:47:28]

Saying "@deprecated" here doesn't have any effect on analysis.  If we want to
deprecate it, we should do:

@deprecated
Token previous;

so that references to it will be flagged by analyzer.

(Note that we can always suppress such warnings using the "// ignore:" syntax)

[danrubel, 2017/03/07 14:40:54]

Good catch. That's what I meant to do. Fixed.

+   * and will be removed at some future date.
+   */
+  Token previous;
+
+  /**
    * Return the first comment in the list of comments that precede this token,
    * or `null` if there are no comments preceding this token. Additional
    * comments can be reached by following the token stream using [next] until