fix test failures on safari 9 and chrome 41 w/focus event

Author: dfreedm

test/unit/shady-events.html

@@ -221,6 +221,12 @@
 
   test('scoped focus and blur events do not retarget', function() {
     var el = fixture('focus');
+    var e = new Event('focus');
+    if (e.isTrused !== false) {
+      // skip browser if we cannot distinguish
+      // native focus events from user created ones
+      this.skip();
+    }
     el.fireScoped();
     assert.equal(el.events.length, 1);
     assert.equal(el.events[0], el.$.child);