Make shadow root clonable attribute read/write (LIKELY ABANDON)

Per the discussion:

whatwg/html#10107

This CL makes `clonable` mutable. It also makes `attachShadow()`
mutate that bit rather than throwing an exception if there's a
mismatching declarative shadow root present. It also makes the
`serializable` bit behave the same way.

Bug: 1510466
Change-Id: Ia3f4b6c18677c7f3d3acd52ba74ea0eb4a31849a

Author: mfreed7

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

@@ -165,6 +165,29 @@
 }, 'Declarative Shadow DOM: clonable attribute');
 </script>
 
+test(() => {
+  const div = document.createElement('div');
+  div.setHTMLUnsafe(`
+    <div id="host">
+      <template shadowrootmode="open" shadowrootclonable>
+      </template>
+    </div>
+    `);
+  var host = div.querySelector('#host');
+  assert_true(!!host.shadowRoot,"No shadow root found");
+  assert_true(host.shadowRoot.clonable,"clonable should be true");
+  div.setHTMLUnsafe(`
+    <div id="host">
+      <template shadowrootmode="open">
+      </template>
+    </div>
+    `);
+  host = div.querySelector('#host');
+  assert_true(!!host.shadowRoot,"No shadow root found");
+  assert_false(host.shadowRoot.clonable,"clonable should be false without the shadowrootclonable attribute");
+}, 'Declarative Shadow DOM: clonable attribute');
+</script>
+
 <div id="multi-host" style="display:none">
   <template shadowrootmode="open">
     <span>root 1</span>

shadow-dom/declarative/declarative-shadow-dom-repeats.html shadow-dom/declarative/declarative-shadow-dom-repeats.tentative.html

@@ -49,30 +49,36 @@
 </script>
 
 <div id=open2>
-  <template shadowrootmode=open shadowrootdelegatesfocus shadowrootclonable>
+  <template shadowrootmode=open shadowrootdelegatesfocus shadowrootclonable serializable>
     Open, delegates focus (not the default), clonable (not the default)
-    named slot assignment (the default)
+    serializable (not the default), named slot assignment (the default)
   </template>
 </div>
 
 <script>
 test((t) => {
+  // These should match the declarative shadow root above.
+  const originalProps = {mode: "open", delegatesFocus: true, slotAssignment: "named", clonable: true, serializable: true};
+
+  // Changing these should throw.
   assert_throws_dom("NotSupportedError",() => {
-    open2.attachShadow({mode: "closed", delegatesFocus: true, slotAssignment: "named", clonable: true});
+    open2.attachShadow({...originalProps, mode: "closed"});
   },'Mismatched shadow root type should throw');
   assert_throws_dom("NotSupportedError",() => {
-    open2.attachShadow({mode: "open", delegatesFocus: false, slotAssignment: "named", clonable: true});
+    open2.attachShadow({...originalProps, delegatesFocus: false});
   },'Mismatched shadow root delegatesFocus should throw');
   assert_throws_dom("NotSupportedError",() => {
-    open2.attachShadow({mode: "open", delegatesFocus: true, slotAssignment: "manual", clonable: true});
+    open2.attachShadow({...originalProps, slotAssignment: "manual"});
   },'Mismatched shadow root slotAssignment should throw');
-  assert_throws_dom("NotSupportedError",() => {
-    open2.attachShadow({mode: "open", delegatesFocus: true, slotAssignment: "named", clonable: false});
-  },'Mismatched shadow root clonable should throw');
 
+  // Boolean arguments just update the shadow root, and return the same root.
   const initialShadow = open2.shadowRoot;
-  const shadow = open2.attachShadow({mode: "open", delegatesFocus: true, slotAssignment: "named", clonable: true}); // Shouldn't throw
+  assert_true(open2.shadowRoot.clonable);
+  assert_true(open2.shadowRoot.serializable);
+  const shadow = open2.attachShadow({...originalProps, clonable: false, serializable: false}); // Shouldn't throw
   assert_equals(shadow,initialShadow,'Same shadow should be returned');
   assert_equals(shadow.textContent,'','Shadow should be empty');
+  assert_false(open2.shadowRoot.clonable,'clonable flag should be updated');
+  assert_false(open2.shadowRoot.serializable,'serializable flag should be updated');
 },'Calling attachShadow() on declarative shadow root must match all parameters');
 </script>

shadow-dom/declarative/gethtml.tentative.html

@@ -123,4 +123,14 @@
 
 runAllTests();
 
+test(() => {
+  const wrapper = document.createElement("div");
+  const div = wrapper.appendChild(document.createElement("div"));
+  const shadow = div.attachShadow({mode: "open", serializable: false});
+  assert_false(shadow.serializable);
+  shadow.serializable = true;
+  assert_true(shadow.serializable);
+  assert_equals(wrapper.getHTML({includeShadowRoots: false}),'<div><template shadowrootmode="open" serializable></template></div>');
+}, "serializable is mutable");
+
 </script>

shadow-dom/shadow-root-clonable.html

@@ -67,6 +67,16 @@
   assert_equals(clonedRoot.children.length, 1, "children count");
   assert_equals(clonedRoot.children[0].localName, "input", "children content");
 }, "declarative shadow roots can opt in to clonable with shadowrootclonable");
+
+test(() => {
+  const div = document.createElement("div");
+  const shadow = div.attachShadow({mode: "open", clonable: false});
+  assert_false(shadow.clonable);
+  shadow.clonable = true;
+  assert_true(shadow.clonable);
+  const clone = div.cloneNode(true);
+  assert_true(!!clone.shadowRoot);
+}, "clonable is mutable");
 </script>
 
 <template id="test">