Stop using the Hashable interface.

lib/compiler/implementation/dart_backend/placeholder_collector.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 LocalPlaceholder implements Hashable {
+class LocalPlaceholder {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
   int hashCode() => identifier.hashCode();
   String toString() =>
       'local_placeholder[id($identifier), nodes($nodes)]';
 }
 
 class FunctionScope {
   final Set<String> parameterIdentifiers;
@@ skipping 409 matching lines @@
     if (currentElement is TypeDeclarationElement) {
       typeDeclarationElement = currentElement;
     } else {
       typeDeclarationElement = currentElement.getEnclosingClass();
     }
     if (typeDeclarationElement !== null && isPlainTypeName(node)
         && tryResolveAndCollectTypeVariable(
                typeDeclarationElement, node.typeName)) {
       return;
     }
-    // We call [resolveReturnType] to allow having 'void'.    
+    // We call [resolveReturnType] to allow having 'void'.
     final type = compiler.resolveReturnType(currentElement, node);
     if (type is InterfaceType || type is TypedefType) {
       Node target = node.typeName;
       bool hasPrefix = false;
       if (node.typeName is Send) {
         final element = treeElements[node];
         if (element !== null) {
           final send = node.typeName.asSend();
           Identifier receiver = send.receiver;
           Identifier selector = send.selector;
@@ skipping 157 matching lines @@
 
   visitBlock(Block node) {
     for (Node statement in node.statements.nodes) {
       if (statement is VariableDefinitions) {
         makeVarDeclarationTypePlaceholder(statement);
       }
     }
     node.visitChildren(this);
   }
 }