use js_ast instead of strings to generate JS

test/codegen/expect/methods/methods.js

 var methods;
-(function (methods) {
+(function(methods) {
   'use strict';
   class A extends dart.Object {
     A() {
       this._c = 3;
     }
-    x() { return 42; }
+    x() {
+      return 42;
+    }
     y(a) {
       return a;
     }
     z(b) {
-      if (b === undefined) b = null;
-      return dart.notNull(b)
+      if (b === void 0)
+        b = null;
+      return dart.notNull(b);
     }
     zz(b) {
-      if (b === undefined) b = 0;
-      return b
+      if (b === void 0)
+        b = 0;
+      return b;
     }
     w(a, opt$) {
-      let b = opt$.b === undefined ? null : opt$.b;
+      let b = opt$.b === void 0 ? null : opt$.b;
       return dart.notNull(a + dart.notNull(b));
     }
     ww(a, opt$) {
-      let b = opt$.b === undefined ? 0 : opt$.b;
+      let b = opt$.b === void 0 ? 0 : opt$.b;
       return a + b;
     }
-    get a() { return this.x(); }
-    set b(b) {
+    get a() {
+      return this.x();
     }
-    get c() { return this._c; }
+    set b(b) {}
+    get c() {
+      return this._c;
+    }
     set c(c) {
       this._c = c;
     }
   }
-
   class Bar extends dart.Object {
-    call(x) { return core.print(`hello from ${x}`); }
+    call(x) {
+      return core.print(`hello from ${x}`);
+    }
   }
-
   class Foo extends dart.Object {
     Foo() {
       this.bar = new Bar();
     }
   }
-
   // Function test: () → dynamic
   function test() {
     let f = new Foo();
-    dart.dinvoke(f, "bar", "Bar's call method!");
+    dart.dinvoke(f, 'bar', "Bar's call method!");
   }
-
   // Exports:
   methods.A = A;
   methods.Bar = Bar;
   methods.Foo = Foo;
   methods.test = test;
 })(methods || (methods = {}));