Make tests call CustomElements.takeRecords to ensure they work in IE where MO polyfill is slightly flaky
super requires __proto__. Simulate this in *test* where unsupported.
Temporarily remove failing mdv syntax test, blocked on https://github.com/Polymer/ShadowDOM/issues/189
Improve IE compatibility by ensuring the __proto__ chain always exists.

In conjunction with https://github.com/Polymer/CustomElements/commit/9b4c5df1c34c9401075fbca602064d7552f3d079,
helps address https://github.com/Polymer/polymer/issues/217.