fixes for angular hello: String + and disable broken arg parsing

test/codegen/expect/fieldtest.js

 var fieldtest;
 (function(exports) {
   'use strict';
   class A extends core.Object {
     A() {
       this.x = 42;
     }
   }
   let B$ = dart.generic(function(T) {
     class B extends core.Object {
@@ skipping 25 matching lines @@
     return 123;
   }
   dart.defineLazyProperties(exports, {
     get y() {
       return dart.notNull(compute()) + 444;
     },
     set y(_) {}
   });
   dart.copyProperties(exports, {
     get q() {
-      return core.String['+'](core.String['+']('life, ', 'the universe '), 'and everything');
+      return 'life, ' + 'the universe ' + 'and everything';
     },
     get z() {
       return 42;
     },
     set z(value) {
       exports.y = dart.as(value, core.int);
     }
   });
   // Function main: () → void
   function main() {
     let a = new A();
     foo(a);
     bar(a);
     core.print(baz(a));
   }
   // Exports:
   exports.A = A;
   exports.B$ = B$;
   exports.B = B;
   exports.foo = foo;
   exports.bar = bar;
   exports.baz = baz;
   exports.compute = compute;
   exports.main = main;
 })(fieldtest || (fieldtest = {}));