Document the Quick View browser test helpers

Now the Quick View browser test suite has been optimized for speed, we
can finish off by documenting the Quick View test JS. Two test helpers
only lack documentation: document what they do.

Comment only change: no change in behavior, no new tests.

Bug: 851888
Change-Id: If87c49919cdd3bd51fa35f714130fc74fb84b543
Reviewed-on: https://chromium-review.googlesource.com/1105530Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568419}

ui/file_manager/integration_tests/file_manager/quick_view.js

@@ -4,6 +4,14 @@
 
 'use strict';
 
+/**
+ * Returns an array of steps that opens the Quick View dialog on a given file
+ * |name|. The file must be present in the Files app file list.
+ *
+ * @param {string} appId Files app windowId.
+ * @param {string} name File name.
+ * @return {!Array<function>}
+ */
 function openQuickViewSteps(appId, name) {
   let caller = getCaller();
 
@@ -39,6 +47,13 @@ function openQuickViewSteps(appId, name) {
   ];
 }
 
+/**
+ * Assuming that Quick View is currently open per the openQuickViewSteps above,
+ * returns an array of steps that closes the Quick View dialog.
+ *
+ * @param {string} appId Files app windowId.
+ * @return {!Array<function>}
+ */
 function closeQuickViewSteps(appId) {
   let caller = getCaller();