Handle dynamic as bottom inside of function type reps

test/codegen/expect/methods.js

 dart_library.library('methods', null, /* Imports */[
   "dart_runtime/dart",
   'dart/core'
 ], /* Lazy imports */[
 ], function(exports, dart, core) {
   'use strict';
   let dartx = dart.dartx;
   let _c = Symbol('_c');
   class A extends core.Object {
     A() {
@@ skipping 43 matching lines @@
       w: [core.int, [core.int], {b: core.num}],
       ww: [core.int, [core.int], {b: core.int}]
     })
   });
   class Bar extends core.Object {
     call(x) {
       return core.print(`hello from ${x}`);
     }
   }
   dart.setSignature(Bar, {
-    methods: () => ({call: [core.Object, [core.Object]]})
+    methods: () => ({call: [dart.dynamic, [dart.dynamic]]})
   });
   class Foo extends core.Object {
     Foo() {
       this.bar = new Bar();
     }
   }
   function test() {
     let f = new Foo();
     dart.dcall(f.bar, "Bar's call method!");
     let a = new A();
     let g = dart.bind(a, 'x');
     let aa = new A();
     let h = dart.dload(aa, 'x');
   }
   dart.fn(test);
   // Exports:
   exports.A = A;
   exports.Bar = Bar;
   exports.Foo = Foo;
   exports.test = test;
 });