Stop using the Hashable interface.

tools/utils/vim/syntax/dart.vim

 " Vim syntax file " Language: 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.
 
 " Quit when a syntax file was already loaded
 if !exists("main_syntax")
   if version < 600
     syntax clear
   elseif exists("b:current_syntax")
     finish
   endif
   " we define it here so that included files can test for it
   let main_syntax='dart'
   syn region dartFold start="{" end="}" transparent fold
 endif
 
 " keyword definitions
 syn keyword dartConditional    if else switch
 syn keyword dartRepeat         do while for
 syn keyword dartBoolean        true false
 syn keyword dartConstant       null
 syn keyword dartTypedef        this super class typedef
 syn keyword dartOperator       new is in factory const
 syn match   dartOperator       "+=\=\|-=\=\|*=\=\|/=\=\|%=\=\|\~/=\=\|<<=\=\|>>=\=\|[<>]=\=\|===\=\|\!==\=\|&=\=\|\^=\=\||=\=\|||\|&&\|\[\]=\=\|=>\|!\|\~"
 syn keyword dartType           void var final bool int double num
 syn keyword dartCommonInterfaces String Object Math RegExp Date
-syn keyword dartInterfaces       Collection Comparable Completer Duration Dynamic Function Future Hashable HashMap HashSet Iterable Iterator LinkedHashMap List Map Match Options Pattern Queue Set Stopwatch StringBuffer TimeZone
+syn keyword dartInterfaces       Collection Comparable Completer Duration Dynamic Function Future HashMap HashSet Iterable Iterator LinkedHashMap List Map Match Options Pattern Queue Set Stopwatch StringBuffer TimeZone
 syn keyword dartErrors         AssertionError TypeError FallThroughError
 syn keyword dartStatement      return
 syn keyword dartStorageClass   static abstract
 syn keyword dartExceptions     throw try catch finally
 syn keyword dartExceptions     BadNumberFormatException ClosureArgumentMismatchException EmptyQueueException Exception ExpectException FutureAlreadyCompleteException FutureNotCompleteException IllegalAccessException ArgumentError IllegalJSRegExpException IndexOutOfRangeException IntegerDivisionByZeroException NoMoreElementsException NoSuchMethodError NotImplementedException NullPointerException ObjectNotClosureException OutOfMemoryException StackOverflowException UnsupportedOperationException WrongArgumentCountException
 syn keyword dartAssert         assert
 syn keyword dartClassDecl      extends implements interface
 " TODO(antonm): check if labels on break and continue are supported.
 syn keyword dartBranch         break continue nextgroup=dartUserLabelRef skipwhite
 syn keyword dartKeyword        get set operator call equals negate external
@@ skipping 65 matching lines @@
   unlet main_syntax
 endif
 
 let b:spell_options="contained"
 
 " Enable automatic indentation (2 spaces)
 set expandtab
 set shiftwidth=2
 set softtabstop=2
 set cindent