Add shadowRootDelegatesFocus and shadowRootClonable reflection

The `shadowRootDelegatesFocus` IDL is standardized [1], and was just
never added to Chromium. This CL lands this addition behind a kill
switch, but should be very safe to add.

The `shadowRootClonable` IDL is being added as part of [2], which
has support and should land soon.

[1] https://html.spec.whatwg.org/multipage/scripting.html#htmltemplateelement
[2] whatwg/html#10117

Bug: 1510466
Change-Id: I708ec8d562fa4d0fc59c73a071dbb191e1bd276e

shadow-dom/declarative/declarative-shadow-dom-basic.html

@@ -54,6 +54,49 @@
   t.getAttribute('shadowrootmode', 'CLOSED');
 }, 'Shadowrootmode reflection, setter');
 
+test(() => {
+  const t = document.createElement('template');
+  t.setAttribute('shadowrootdelegatesfocus','');
+  assert_equals(t.shadowRootDelegatesFocus,true,'The shadowRootDelegatesFocus IDL should reflect the content attribute');
+  t.setAttribute('shadowrootdelegatesfocus','foobar');
+  assert_equals(t.shadowRootDelegatesFocus,true,'The value doesn\'t matter');
+  t.removeAttribute('shadowrootdelegatesfocus');
+  assert_equals(t.shadowRootDelegatesFocus,false,'No shadowRootDelegatesFocus attribute maps to false');
+}, 'Shadowrootdelegatesfocus reflection');
+
+test(() => {
+  const t = document.createElement('template');
+  assert_equals(t.getAttribute('shadowrootdelegatesfocus'), null);
+  t.shadowRootDelegatesFocus = true;
+  assert_equals(t.getAttribute('shadowrootdelegatesfocus'), '');
+  assert_equals(t.shadowRootDelegatesFocus, true);
+  t.shadowRootDelegatesFocus = false;
+  assert_equals(t.getAttribute('shadowrootdelegatesfocus'), null);
+  assert_equals(t.shadowRootDelegatesFocus, false);
+}, 'Shadowrootdelegatesfocus reflection, setter');
+
+
+test(() => {
+  const t = document.createElement('template');
+  t.setAttribute('shadowrootclonable','');
+  assert_equals(t.shadowRootClonable,true,'The shadowRootClonable IDL should reflect the content attribute');
+  t.setAttribute('shadowrootclonable','foobar');
+  assert_equals(t.shadowRootClonable,true,'The value doesn\'t matter');
+  t.removeAttribute('shadowrootclonable');
+  assert_equals(t.shadowRootClonable,false,'No shadowRootClonable attribute maps to false');
+}, 'Shadowrootclonable reflection');
+
+test(() => {
+  const t = document.createElement('template');
+  assert_equals(t.getAttribute('shadowrootclonable'), null);
+  t.shadowRootClonable = true;
+  assert_equals(t.getAttribute('shadowrootclonable'), '');
+  assert_equals(t.shadowRootClonable, true);
+  t.shadowRootClonable = false;
+  assert_equals(t.getAttribute('shadowrootclonable'), null);
+  assert_equals(t.shadowRootClonable, false);
+}, 'Shadowrootclonable reflection, setter');
+
 test(() => {
   const div = document.createElement('div');
   div.setHTMLUnsafe(`