Dartium: implement IDBKeyRange constructors

[rakudrama]

See https://chromiumcodereview.appspot.com/10151002/ for dart2js and partial dartium code

Test: dom/IndexedDB4Test.dart

[DartBot]

This comment was originally written by antonm@google.com

---

Added Started label.

[DartBot]

This comment was originally written by antonm@google.com

---

Added this to the M1 milestone.

[DartBot]

This comment was originally written by antonm@google.com

---

Added Fixed label.