Stop using the Hashable interface.

lib/compiler/implementation/typechecker.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.
 
 class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
   String get name => "Type checker";
 
   static const bool LOG_FAILURES = false;
 
   void check(Node tree, TreeElements elements) {
     measure(() {
       Visitor visitor =
           new TypeCheckerVisitor(compiler, elements, compiler.types);
       try {
         tree.accept(visitor);
       } on CancelTypeCheckException catch (e) {
         if (LOG_FAILURES) {
           // Do not warn about unimplemented features; log message instead.
           compiler.log("'${e.node}': ${e.reason}");
         }
       }
     });
   }
 }
 
-abstract class DartType implements Hashable {
+abstract class DartType {
   abstract SourceString get name;
   /**
    * Returns the [Element] which declared this type.
    *
    * This can be [ClassElement] for classes, [TypedefElement] for typedefs,
    * [TypeVariableElement] for type variables and [FunctionElement] for
    * function types.
    *
    * Invariant: [element] must be a declaration element.
    */
@@ skipping 879 matching lines @@
   }
 
   visitCatchBlock(CatchBlock node) {
     return unhandledStatement();
   }
 
   visitTypedef(Typedef node) {
     return unhandledStatement();
   }
 }