add more reliable source-map tests

test/fixtures/source-maps/class/expected.js

@@ -0,0 +1,16 @@
+var Test = function() {
+  function Test() {}
+
+  Object.defineProperties(Test.prototype, {
+    bar: {
+      get: function() {
+        throw new Error("wow");
+      }
+    }
+  });
+
+  return Test;
+}();
+
+var test = new Test;
+test.bar;