In JsonEncoder, test if map has only string keys, and use toEncodable if not.

tests/lib/convert/json_toEncodable_reviver_test.dart

Index: tests/lib/convert/json_toEncodable_reviver_test.dart
diff --git a/tests/lib/convert/json_toEncodable_reviver_test.dart b/tests/lib/convert/json_toEncodable_reviver_test.dart
index 58438875832ba8af0ec99feb114e2914d174648b..0c0be3e30c3932d6c9a2f7a52114fe50596874fe 100644
--- a/tests/lib/convert/json_toEncodable_reviver_test.dart
+++ b/tests/lib/convert/json_toEncodable_reviver_test.dart
@@ -38,4 +38,18 @@ main() {
   var a = extendedJson.decode(extendedJson.encode(new A(499)));
   Expect.isTrue(a is A);
   Expect.equals(499, a.x);
+
+  testInvalidMap();
+}
+
+
+void testInvalidMap() {
+  var map = {"a" : 42, "b": 42, 37: 42};  // Non-string key.
+  var enc = new JsonEncoder((x) => "fixed");

[Søren Gjesse, 2015/05/27 08:45:04]

x -> _

+  var res = enc.convert(map);
+  Expect.equals('"fixed"', res);
+
+  enc = new JsonEncoder.withIndent(" ", (_) => "fixed");
+  res = enc.convert(map);
+  Expect.equals('"fixed"', res);
 }