Don't dispatch synthetic events if target == relatedTarget

Revert the part of https://codereview.chromium.org/2384403002
since the DOM Standard was updated and 'isTrusted' guard condition was removed from there.

See the discussion at whatwg/dom#336 for details.

Blink forgot to address the update of the commit, as mentioned at
whatwg/dom#336 (comment).

Bug: 655494
Change-Id: I084cd6b748c304f5f2b395f0b62ba02025385a98

Author: hayatoito

shadow-dom/event-composed-path-with-related-target.html

@@ -25,9 +25,8 @@
   let n = createTestTree(test1);
   let log = dispatchEventWithLog(n, n.target, new FocusEvent('my-focus', { bubbles: true, composed: true, relatedTarget: n.target }));
   let path = ['target', 'test1'];
-  assert_event_path_equals(log, [['target', 'target', 'target', path],
-                                 ['test1', 'target', 'target', path]]);
-}, 'Event path for an event with a relatedTarget. Event should be dispatched even when target and relatedTarget are same.');
+  assert_array_equals(log, []);
+}, 'Event path for an event with a relatedTarget. Event should not be dispatched when target and relatedTarget are same.');
 </script>
 
 <div id="test2">
@@ -52,9 +51,8 @@
   let n = createTestTree(test2);
   let log = dispatchEventWithLog(n, n.target, new FocusEvent('my-focus', { bubbles: true, composed: true, relatedTarget: n.target }));
   let path = ['target', 'sr'];
-  assert_event_path_equals(log, [['target', 'target', 'target', path],
-                                 ['sr', 'target', 'target', path]]);
-}, 'Event path for an event with a relatedTarget which is identical to target. Event should be dispatched and should stop at the shadow root.');
+  assert_array_equals(log, []);
+}, 'Event path for an event with a relatedTarget which is identical to target. Event should not be dispatched.');
 </script>
 
 <div id="test3_1">
@@ -137,8 +135,7 @@
   let n = createTestTree(test4);
   let log = dispatchEventWithLog(n, n.host1, new FocusEvent('my-focus', { bubbles: true, composed: true, relatedTarget: n.target }));
   let path = ['host1', 'test4'];
-  assert_event_path_equals(log, [['host1', 'host1', 'host1', path],
-                                 ['test4', 'host1', 'host1', path]]);
+  assert_event_path_equals(log, []);
 }, 'Event path for an event with a relatedTarget. target is a shadow-including ancestor of relatedTarget.');
 </script>