Handle dynamic as bottom inside of function type reps

test/codegen/expect/fieldtest.js

 dart_library.library('fieldtest', null, /* Imports */[
   "dart_runtime/dart",
   'dart/core'
 ], /* Lazy imports */[
 ], function(exports, dart, core) {
   'use strict';
   let dartx = dart.dartx;
   class A extends core.Object {
     A() {
       this.x = 42;
@@ skipping 12 matching lines @@
   let B = B$();
   function foo(a) {
     core.print(a.x);
     return a.x;
   }
   dart.fn(foo, core.int, [A]);
   function bar(a) {
     core.print(dart.dload(a, 'x'));
     return dart.as(dart.dload(a, 'x'), core.int);
   }
-  dart.fn(bar, core.int, [core.Object]);
+  dart.fn(bar, core.int, [dart.dynamic]);
   function baz(a) {
     return a.x;
   }
-  dart.fn(baz, core.Object, [A]);
+  dart.fn(baz, dart.dynamic, [A]);
   function compute() {
     return 123;
   }
   dart.fn(compute, core.int, []);
   dart.defineLazyProperties(exports, {
     get y() {
       return dart.notNull(compute()) + 444;
     },
     set y(_) {}
   });
@@ skipping 21 matching lines @@
   }
   dart.virtualField(Derived, 'foo');
   let Generic$ = dart.generic(function(T) {
     class Generic extends core.Object {
       foo(t) {
         dart.as(t, T);
         return core.print(dart.notNull(Generic$().bar) + dart.notNull(dart.as(t, core.String)));
       }
     }
     dart.setSignature(Generic, {
-      methods: () => ({foo: [core.Object, [T]]})
+      methods: () => ({foo: [dart.dynamic, [T]]})
     });
     return Generic;
   });
   let Generic = Generic$();
   Generic.bar = 'hello';
   class StaticFieldOrder1 extends core.Object {}
   StaticFieldOrder1.d = 4;
   StaticFieldOrder1.c = dart.notNull(StaticFieldOrder1.d) + 2;
   StaticFieldOrder1.b = dart.notNull(StaticFieldOrder1.c) + 3;
   StaticFieldOrder1.a = dart.notNull(StaticFieldOrder1.b) + 1;
@@ skipping 19 matching lines @@
   exports.baz = baz;
   exports.compute = compute;
   exports.BaseWithGetter = BaseWithGetter;
   exports.Derived = Derived;
   exports.Generic$ = Generic$;
   exports.Generic = Generic;
   exports.StaticFieldOrder1 = StaticFieldOrder1;
   exports.StaticFieldOrder2 = StaticFieldOrder2;
   exports.main = main;
 });