Missing test from CL 10544173.

dart/lib/compiler/implementation/scanner/scanner.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 interface Scanner {
   Token tokenize();
 }
 
 /**
  * Common base class for a Dart scanner.
@@ skipping 18 matching lines @@
   abstract int get charOffset();
   abstract int get byteOffset();
   abstract void appendBeginGroup(PrecedenceInfo info, String value);
   abstract int appendEndGroup(PrecedenceInfo info, String value, int openKind);
   abstract void appendGt(PrecedenceInfo info, String value);
   abstract void appendGtGt(PrecedenceInfo info, String value);
   abstract void appendGtGtGt(PrecedenceInfo info, String value);
 
   /**
    * We call this method to discard '<' from the "grouping" stack
-   * (maintained by subclasses). That we don't create groups for stuff
-   * like "a = b < c, d = e > f" is used by
-   * [PartialParser.skipExpression].
+   * (maintained by subclasses).
+   *
+   * [PartialParser.skipExpression] relies on the fact that we do not
+   * create groups for stuff like:
+   * [:a = b < c, d = e > f:].
+   *
+   * In other words, this method is called when the scanner recognizes
+   * something which cannot possibly be part of a type
+   * parameter/argument list.
    */
   abstract void discardOpenLt();
 
   // TODO(ahe): Move this class to implementation.
 
   Token tokenize() {
     int next = advance();
     while (next !== $EOF) {
       next = bigSwitch(next);
     }
@@ skipping 722 matching lines @@
                                       charOffset);
   }
 }
 
 class MalformedInputException {
   final String message;
   final position;
   MalformedInputException(this.message, this.position);
   toString() => message;
 }