Add upstream

wp-content/plugins/jetpack/_inc/accessible-focus.js

@@ -0,0 +1,19 @@
+var keyboardNavigation = false,
+	keyboardNavigationKeycodes = [ 9, 32, 37, 38, 39, 40 ]; // keyCodes for tab, space, left, up, right, down respectively
+
+document.addEventListener( 'keydown', function( event ) {
+	if ( keyboardNavigation ) {
+		return;
+	}
+	if ( keyboardNavigationKeycodes.indexOf( event.keyCode ) !== -1 ) {
+		keyboardNavigation = true;
+		document.documentElement.classList.add( 'accessible-focus' );
+	}
+} );
+document.addEventListener( 'mouseup', function() {
+	if ( ! keyboardNavigation ) {
+		return;
+	}
+	keyboardNavigation = false;
+	document.documentElement.classList.remove( 'accessible-focus' );
+} );