kernel->ssa: support string concatenations/interpolations

tests/compiler/dart2js/kernel/literals_test.dart

Index: tests/compiler/dart2js/kernel/literals_test.dart
diff --git a/tests/compiler/dart2js/kernel/literals_test.dart b/tests/compiler/dart2js/kernel/literals_test.dart
index bf849892226dc7439e4ad107efc3a6f5bb7d63ff..4bdf2714bb1726976ae857102f660f2f3fb49eac 100644
--- a/tests/compiler/dart2js/kernel/literals_test.dart
+++ b/tests/compiler/dart2js/kernel/literals_test.dart
@@ -16,7 +16,7 @@ main() {
   test('compile function that returns a literal map', () {
     return check('main() { return {"a": 1, "b": 2, "c": 3}; }');
   });
-  test('compile function that returns a literal map', () {
+  test('compile function that returns a const map', () {
     return check('main() { return const {"a": 1, "b": 2, "c": 3}; }');
   });
 }