kernel -> ssa: implement literal maps

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 5e3a0a660cfaa5cbb99b1d638a239bc277f2c6a6..bf849892226dc7439e4ad107efc3a6f5bb7d63ff 100644
--- a/tests/compiler/dart2js/kernel/literals_test.dart
+++ b/tests/compiler/dart2js/kernel/literals_test.dart
@@ -13,4 +13,10 @@ main() {
   test('compile function that returns a const list', () {
     return check('main() { return const [1, 2, 3]; }');
   });
+  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', () {
+    return check('main() { return const {"a": 1, "b": 2, "c": 3}; }');
+  });
 }