Serialize delegatesFocus in getInnerHTML()

Prior to this CL, the getInnerHTML() call with includeShadowRoots=true
would not return markup with the shadowrootdelegatesfocus attribute.
Now, it does, and testing has been added to verify this behavior.

Bug: 1042130
Change-Id: Ibd859af110328b965e4c9a0074095a5a1e5251b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2285288
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Auto-Submit: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786393}

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

@@ -38,6 +38,7 @@
         // TODO(masonfreed): Add a check for ElementInternals.shadowRoot once that exists.
         assert_true(!!element.shadowRoot, 'Shadow root should be present');
         assert_equals(element.shadowRoot.innerHTML, shadowContent, 'Correct shadow content');
+        assert_equals(element.shadowRoot.delegatesFocus,delegatesFocus,'Correct delegatesFocus')
         originalShadowRoot = element.shadowRoot;
       }
 

shadow-dom/declarative/getinnerhtml.tentative.html

@@ -20,7 +20,8 @@
 
     const isOpen = mode === 'open';
     if (allowsShadowDom) {
-      const correctShadowHtml = `<template shadowroot="${mode}"><slot></slot></template>`;
+      const delegatesAttr = delegatesFocus ? ' shadowrootdelegatesfocus=""' : '';
+      const correctShadowHtml = `<template shadowroot="${mode}"${delegatesAttr}><slot></slot></template>`;
       const correctHtml = `<${elementType}>${correctShadowHtml}</${elementType}>`;
       const shadowRoot = element.attachShadow({mode: mode, delegatesFocus: delegatesFocus});
       shadowRoot.appendChild(document.createElement('slot'));