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

lib/runtime/dart/_internal.js

 dart_library.library('dart/_internal', null, /* Imports */[
   'dart/_runtime',
   'dart/core',
   'dart/collection'
 ], /* Lazy imports */[
   'dart/math',
   'dart/_interceptors',
   'dart/_js_primitives'
 ], function(exports, dart, core, collection, math, _interceptors, _js_primitives) {
   'use strict';
@@ skipping 580 matching lines @@
   });
   let _ExpandFunction = _ExpandFunction$();
   const ExpandIterable$ = dart.generic(function(S, T) {
     class ExpandIterable extends collection.IterableBase$(T) {
       ExpandIterable(iterable, f) {
         this[_iterable] = iterable;
         this[_f] = f;
         super.IterableBase();
       }
       get iterator() {
-        return new (ExpandIterator$(S, T))(this[_iterable][dartx.iterator], dart.as(this[_f], __CastType0));
+        return new (ExpandIterator$(S, T))(this[_iterable][dartx.iterator], dart.as(this[_f], dart.functionType(core.Iterable$(T), [S])));
       }
     }
     dart.setSignature(ExpandIterable, {
       constructors: () => ({ExpandIterable: [ExpandIterable$(S, T), [core.Iterable$(S), dart.functionType(core.Iterable$(T), [S])]]})
     });
     dart.defineExtensionMembers(ExpandIterable, ['iterator']);
     return ExpandIterable;
   });
   let ExpandIterable = ExpandIterable$();
   const _currentExpansion = dart.JsSymbol('_currentExpansion');
@@ skipping 649 matching lines @@
         return new MappedListIterable(list, f);
       }
       static expand(iterable, f) {
         return new ExpandIterable(iterable, f);
       }
       takeList(list, n) {
         return new (SubListIterable$(T))(dart.as(list, core.Iterable$(T)), 0, n);
       }
       takeWhile(iterable, test) {
         dart.as(test, dart.functionType(core.bool, [dart.dynamic]));
-        return new (TakeWhileIterable$(T))(dart.as(iterable, core.Iterable$(T)), dart.as(test, __CastType2));
+        return new (TakeWhileIterable$(T))(dart.as(iterable, core.Iterable$(T)), dart.as(test, dart.functionType(core.bool, [T])));
       }
       skipList(list, n) {
         return new (SubListIterable$(T))(dart.as(list, core.Iterable$(T)), n, null);
       }
       skipWhile(iterable, test) {
         dart.as(test, dart.functionType(core.bool, [dart.dynamic]));
         return new (SkipWhileIterable$(T))(dart.as(iterable, core.Iterable$(T)), dart.as(test, dart.functionType(core.bool, [T])));
       }
       reversedList(list) {
         return new (ReversedListIterable$(T))(dart.as(list, core.Iterable$(T)));
@@ skipping 208 matching lines @@
     }
   }
   dart.setSignature(IterableElementError, {
     statics: () => ({
       noElement: [core.StateError, []],
       tooMany: [core.StateError, []],
       tooFew: [core.StateError, []]
     }),
     names: ['noElement', 'tooMany', 'tooFew']
   });
-  const __CastType0$ = dart.generic(function(S, T) {
-    const __CastType0 = dart.typedef('__CastType0', () => dart.functionType(core.Iterable$(T), [S]));
-    return __CastType0;
-  });
-  let __CastType0 = __CastType0$();
-  const __CastType2$ = dart.generic(function(T) {
-    const __CastType2 = dart.typedef('__CastType2', () => dart.functionType(core.bool, [T]));
-    return __CastType2;
-  });
-  let __CastType2 = __CastType2$();
   const FixedLengthListMixin$ = dart.generic(function(E) {
     dart.defineExtensionNames([
       'length',
       'add',
       'insert',
       'insertAll',
       'addAll',
       'remove',
       'removeWhere',
       'retainWhere',
@@ skipping 843 matching lines @@
   exports.ReversedListIterable$ = ReversedListIterable$;
   exports.ReversedListIterable = ReversedListIterable;
   exports.UnmodifiableListError = UnmodifiableListError;
   exports.NonGrowableListError = NonGrowableListError;
   exports.makeListFixedLength = makeListFixedLength;
   exports.Lists = Lists;
   exports.printToConsole = printToConsole;
   exports.Sort = Sort;
   exports.Symbol = Symbol;
 });