implement kernel -> ssa for literals

tests/compiler/dart2js/kernel/simple_function_test.dart

 import 'package:test/test.dart';
 
 import 'helper.dart' show check;
 
 main() {
-  test('compile function that returns a constant', () {
-    return check("main() { return 1; }");
+  group('compile function that returns a value', () {
+    test('constant int', () {
+      return check("main() { return 1; }");
+    });
+
+    test('constant double', () {
+      return check("main() { return 1.0; }");
+    });
+
+    test('constant string', () {
+      return check("main() { return 'hello'; }");
+    });
+
+    test('constant bool', () {
+      return check("main() { return true; }");
+    });
+
+    test('constant symbol', () {
+      return check("main() { return #hello; }");
+    });
+
+    test('null', () {
+      return check("main() { return null; }");
+    });
   });
 }