[Spec compat] form element pointer should be set iff no template element on the stack of open eleme…

third_party/WebKit/LayoutTests/fast/parser/form-in-template.html

+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<script>
+test(function() {
+  let snippet = '<a><form></form><div></div></a>';

[kaizhu256, 2016/11/03 01:23:35]

the test-case can be generalized to
-  let snippet = '<a><form></form><div></div></a>';
+  let snippet = '<form></form><div></div>';

tested the generalized case to fail inside stable chrome's console:

      var snippet = '<form></form><div></div>';
      var templateTag = document.createElement('template');
      templateTag.innerHTML = snippet
      console.assert(templateTag.innerHTML === snippet, "Unexpected reparenting
shouldn't happen.");
      // output:
      // VM131:4 Assertion failed: Unexpected reparenting shouldn't happen.

+  let templateTag = document.createElement('template');
+  templateTag.innerHTML = snippet
+  assert_equals(templateTag.innerHTML, snippet, "Unexpected reparenting shouldn't happen.");
+}, "form inside template tag should be parsed correctly");
+</script>