Accessibility: Skip empty table cells for system info subpage

Improve accessbility for system info subpage of Feedback by
marking empty cells in the table as aria-hidden. This really does
improve the navigation experience.

BUG=chromium:1005567
TEST=Ran system info under ChromeVox. Navigated around page, expanded
and collapsed sections, etc

Change-Id: I6397357552b6c4a78afaafc56a3fd1b4db5e8c1d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1869888Reviewed-by: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: J Kardatzke <jkardatzke@chromium.org>
Commit-Queue: Ian Barkley-Yeung <iby@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707971}

chrome/browser/resources/feedback/js/sys_info.js

@@ -41,6 +41,7 @@ function expand(button, valueDiv, delayFactor) {
   button.textContent = loadTimeData.getString('sysinfoPageCollapseBtn');
   // Show the spinner container.
   const valueCell = valueDiv.parentNode;
+  valueCell.removeAttribute('aria-hidden');
   valueCell.firstChild.hidden = false;
   // Expanding huge logs can take a very long time, so we do it after a delay
   // to have a chance to render the spinner.
@@ -59,6 +60,9 @@ function expand(button, valueDiv, delayFactor) {
 function collapse(button, valueDiv) {
   button.textContent = loadTimeData.getString('sysinfoPageExpandBtn');
   valueDiv.parentNode.className = 'number-collapsed';
+  // Don't have screen readers announce the empty cell.
+  valueCell = valueDiv.parentNode;
+  valueCell.setAttribute('aria-hidden', 'true');
 }
 
 /**
@@ -122,9 +126,13 @@ function createButtonCell(key, isMultiLine) {
   if (isMultiLine) {
     const button = document.createElement('button');
     button.setAttribute('id', '' + key + '-value-btn');
+    button.setAttribute('aria-controls', '' + key + '-value');
     button.onclick = changeCollapsedStatus;
     button.textContent = loadTimeData.getString('sysinfoPageExpandBtn');
     buttonCell.appendChild(button);
+  } else {
+    // Don't have screen reader read the empty cell.
+    buttonCell.setAttribute('aria-hidden', 'true');
   }
 
   return buttonCell;
@@ -143,6 +151,8 @@ function createValueCell(key, value, isMultiLine) {
     loadingContainer.setAttribute('id', '' + key + '-value-loading');
     loadingContainer.hidden = true;
     valueCell.appendChild(loadingContainer);
+    // Don't have screen readers read the empty cell.
+    valueCell.setAttribute('aria-hidden', 'true');
   } else {
     valueCell.className = 'number';
   }