[ios] Adds TableViewLinkHeaderFooterCell accessibilityLabel.

Bug: 979673
Change-Id: I82df2334bff60dd2867e336f7f7a89f9163ebd3e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1750044Reviewed-by: Robbie Gibson <rkgibson@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686439}

ios/chrome/browser/ui/table_view/cells/table_view_link_header_footer_item.mm

@@ -41,6 +41,7 @@ const CGFloat kVerticalPadding = 8;
   [super configureHeaderFooterView:headerFooter withStyler:styler];
 
   headerFooter.linkURL = self.linkURL;
+  headerFooter.accessibilityTraits |= UIAccessibilityTraitLink;
   [headerFooter setText:self.text];
 }
 
@@ -141,4 +142,10 @@ const CGFloat kVerticalPadding = 8;
   return NO;
 }
 
+#pragma mark - NSObject(Accessibility)
+
+- (NSString*)accessibilityLabel {
+  return [self.textView.attributedText string];
+}
+
 @end