Remove as checks bloating sample dart apps by 4K

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 9307474d0d3881209c75ef003dc9fc0b86a98ad3..ccc652dbea2f2c81c4d15fbd261d1dd0dac4a854 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -47866,7 +47866,10 @@ _wrapZoneCallback/*<A, R>*/ _wrapZone/*<A, R>*/(_wrapZoneCallback/*<A, R>*/ call
   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) {
@@ -47874,7 +47877,10 @@ _wrapZoneBinaryCallback/*<A, B, R>*/ _wrapBinaryZone/*<A, B, R>*/(_wrapZoneBinar
   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;
 }
 
 /**