coverage: increase coverage of js_codegen

test/codegen/map_keys.dart

Index: test/codegen/map_keys.dart
diff --git a/test/codegen/map_keys.dart b/test/codegen/map_keys.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e03862ba5ea2dbe2f68a4564633ad15007d5f29b
--- /dev/null
+++ b/test/codegen/map_keys.dart
@@ -0,0 +1,14 @@
+import 'dart:math' show Random;
+main() {
+  // Uses a JS object literal
+  print({ '1': 2, '3': 4, '5': 6 });
+  // Uses array literal
+  print({ 1: 2, 3: 4, 5: 6 });
+  // Uses ES6 enhanced object literal
+  print({ '1': 2, '${new Random().nextInt(2) + 2}': 4, '5': 6 });
+  String x = '3';
+  // Could use enhanced object literal if we knew `x` was not null
+  print({ '1': 2, x: 4, '5': 6 });
+  // Array literal
+  print({ '1': 2, null: 4, '5': 6 });
+}