Remove as checks bloating sample dart apps by 4K

tools/dom/src/shared_html.dart

 // Copyright (c) 2013, 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.
 
 part of dart.dom.html;
 
 // TODO(jacobr): remove these typedefs when dart:async supports generic types.
 typedef R _wrapZoneCallback<A, R>(A a);
 typedef R _wrapZoneBinaryCallback<A, B, R>(A a, B b);
 
 _wrapZoneCallback/*<A, R>*/ _wrapZone/*<A, R>*/(_wrapZoneCallback/*<A, R>*/ callback) {
   // For performance reasons avoid wrapping if we are in the root zone.
   if (Zone.current == Zone.ROOT) return callback;
   if (callback == null) return null;
   // TODO(jacobr): we cast to _wrapZoneCallback/*<A, R>*/ to hack around missing
   // generic method support in zones.
-  return Zone.current.bindUnaryCallback(callback, runGuarded: true) as _wrapZoneCallback/*<A, R>*/;
+  // ignore: STRONG_MODE_DOWN_CAST_COMPOSITE
+  _wrapZoneCallback/*<A, R>*/ wrapped =
+      Zone.current.bindUnaryCallback(callback, runGuarded: true);
+  return wrapped;
 }
 
 _wrapZoneBinaryCallback/*<A, B, R>*/ _wrapBinaryZone/*<A, B, R>*/(_wrapZoneBinaryCallback/*<A, B, R>*/ callback) {
   if (Zone.current == Zone.ROOT) return callback;
   if (callback == null) return null;
   // We cast to _wrapZoneBinaryCallback/*<A, B, R>*/ to hack around missing
   // generic method support in zones.
-  return Zone.current.bindBinaryCallback(callback, runGuarded: true) as _wrapZoneBinaryCallback/*<A, B, R>*/;
+  // ignore: STRONG_MODE_DOWN_CAST_COMPOSITE
+  _wrapZoneBinaryCallback/*<A, B, R>*/ wrapped =
+      Zone.current.bindBinaryCallback(callback, runGuarded: true);
+  return wrapped;
 }
 
 /**
  * Alias for [querySelector]. Note this function is deprecated because its
  * semantics will be changing in the future.
  */
 @deprecated
 @Experimental()
 Element query(String relativeSelectors) => document.query(relativeSelectors);
 /**
@@ skipping 42 matching lines @@
 ElementList<Element> querySelectorAll(String selectors) => document.querySelectorAll(selectors);
 
 /// A utility for changing the Dart wrapper type for elements.
 abstract class ElementUpgrader {
   /// Upgrade the specified element to be of the Dart type this was created for.
   ///
   /// After upgrading the element passed in is invalid and the returned value
   /// should be used instead.
   Element upgrade(Element element);
 }