Require two type arguments for map literals (issue 4522).

samples/webcomponents/shadow_polyfill.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Polyfill script for custom elements. To use this script, your app must
  * create a CustomElementsManager with the appropriate lookup function before
  * doing any DOM queries or modifications.
  * Currently, all custom elements must be registered with the polyfill.  To
  * register custom elements, provide the appropriate lookup function to your
@@ skipping 56 matching lines @@
   // arbitrary Dart objects directly on DOM objects rather than this map.
   /** Maps DOM elements to the user-defiend corresponding dart objects. */
   ListMap<Element, WebComponent> _customElements;
 
   RegistryLookupFunction _lookup;
 
   MutationObserver _insertionObserver;
 
   CustomElementsManager._internal(this._lookup) {
     // TODO(samhop): check for ShadowDOM support
-    _customDeclarations = <_CustomDeclaration>{};
+    _customDeclarations = <String, _CustomDeclaration>{};
     // We use a ListMap because DOM objects aren't hashable right now.
     // TODO(samhop): DOM objects (and everything else) should be hashable
     _customElements = new ListMap<Element, WebComponent>();
     initializeInsertedRemovedCallbacks(document);
   }
 
   /**
    * Locate all external component files, load each of them, and expand
    * declarations.
    */
@@ skipping 250 matching lines @@
       }
     });
     attributeObserver.observe(e, attributes: true, attributeOldValue: true);
 
     // Listen for all insertions and deletions on the DOM so that we can
     // catch custom elements being inserted and call the appropriate callbacks.
     manager.initializeInsertedRemovedCallbacks(shadowRoot);
     return newCustomElement;
   }
 }