fix #29789, avoid unneccessary dcalls and checks in dart:_runtime

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/rtti.dart

 // Copyright (c) 2015, 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.
 
 /// This library defines the association between runtime objects and
 /// runtime types.
 part of dart._runtime;
 
 /// Runtime type information.  This module defines the mapping from
 /// runtime objects to their runtime type information.  See the types
@@ skipping 92 matching lines @@
   if (JS('bool', 'typeof # == "symbol"', obj)) {
     // Note: this is a JS Symbol, not a Dart one.
     return JS('', '#', jsobject);
   }
 
   return null;
 }
 
 getFunctionType(obj) {
   // TODO(vsm): Encode this properly on the function for Dart-generated code.
-  var args = JS('', 'Array(#.length).fill(#)', obj, dynamic);
+  var args = JS('List', 'Array(#.length).fill(#)', obj, dynamic);
   return fnType(bottom, args, JS('', 'void 0'));
 }
 
 /// Returns the runtime representation of the type of obj.
 ///
 /// The resulting object is used internally for runtime type checking. This is
 /// different from the user-visible Type object returned by calling
 /// `runtimeType` on some Dart object.
 getReifiedType(obj) {
   var result = _checkPrimitiveType(obj);
@@ skipping 98 matching lines @@
   if (module == null) return null;
   JS('', '#[#] = #', module, _moduleName, name);
   return module;
 }
 
 /// Track all libraries
 void trackLibraries(String moduleName, libraries, sourceMap) {
   JS('', '#.set(#, #)', _loadedSourceMaps, moduleName, sourceMap);
   JS('', '#.set(#, #)', _loadedModules, moduleName, libraries);
 }