simplify function coercions -- DDC can generate function types in place

lib/runtime/dart/html_common.js

 dart_library.library('dart/html_common', null, /* Imports */[
   'dart/_runtime',
   'dart/_metadata',
   'dart/core',
   'dart/html',
   'dart/typed_data',
   'dart/_js_helper',
   'dart/_native_typed_data',
   'dart/async',
   'dart/_internal',
@@ skipping 91 matching lines @@
       if (!(typeof value == 'string')) return false;
       let s = this.readClasses();
       let result = s.remove(value);
       this.writeClasses(s);
       return result;
     }
     addAll(iterable) {
       this.modify(dart.fn(s => s.addAll(iterable[dartx.map](dart.bind(this, _validateToken))), dart.void, [core.Set$(core.String)]));
     }
     removeAll(iterable) {
-      this.modify(dart.fn(s => s.removeAll(iterable[dartx.map](dart.as(dart.bind(this, _validateToken), __CastType0))), dart.void, [core.Set$(core.String)]));
+      this.modify(dart.fn(s => s.removeAll(iterable[dartx.map](dart.as(dart.bind(this, _validateToken), dart.functionType(core.String, [core.Object])))), dart.void, [core.Set$(core.String)]));
     }
     toggleAll(iterable, shouldAdd) {
       if (shouldAdd === void 0) shouldAdd = null;
       iterable[dartx.forEach](dart.fn(e => this.toggle(e, shouldAdd), core.bool, [core.String]));
     }
     retainAll(iterable) {
       this.modify(dart.fn(s => s.retainAll(iterable), dart.void, [core.Set$(core.String)]));
     }
     removeWhere(test) {
       this.modify(dart.fn(s => s.removeWhere(test), dart.void, [core.Set$(core.String)]));
@@ skipping 134 matching lines @@
     'length',
     'first',
     'last',
     'single'
   ]);
   dart.defineLazyProperties(CssClassSetImpl, {
     get _validTokenRE() {
       return core.RegExp.new('^\\S+$');
     }
   });
-  const __CastType0 = dart.typedef('__CastType0', () => dart.functionType(core.String, [core.Object]));
   function convertDartToNative_SerializedScriptValue(value) {
     return convertDartToNative_PrepareForStructuredClone(value);
   }
   dart.fn(convertDartToNative_SerializedScriptValue);
   function convertNativeToDart_SerializedScriptValue(object) {
     return convertNativeToDart_AcceptStructuredClone(object, {mustCopy: true});
   }
   dart.fn(convertNativeToDart_SerializedScriptValue);
   class _StructuredClone extends core.Object {
     _StructuredClone() {
@@ skipping 673 matching lines @@
   exports.isImmutableJavaScriptArray = isImmutableJavaScriptArray;
   exports.isJavaScriptPromise = isJavaScriptPromise;
   exports.convertNativePromiseToDartFuture = convertNativePromiseToDartFuture;
   exports.wrap_jso = wrap_jso;
   exports.unwrap_jso = unwrap_jso;
   exports.Device = Device;
   exports.FilteredElementList = FilteredElementList;
   exports.Lists = Lists;
   exports.NodeListWrapper = NodeListWrapper;
 });