Clean up transfer.js browser test

Clean up transfer.js browser test, and generalize it to transfer between
different sources and destinations, move and copy and allow transfer
failures.

This is pre-work to add tests for all the possible transfer behavior
operations.

Bug: 722324
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: Ib1d43a9fe1b7160fe9c93ec10c8cfb1c460889e0
Reviewed-on: https://chromium-review.googlesource.com/1128660
Commit-Queue: Sasha Morrissey <sashab@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576303}

ui/file_manager/file_manager/background/js/test_util.js

@@ -119,7 +119,7 @@ test.util.sync.openFile = function(contentWindow, filename) {
 };
 
 /**
- * Selects a volume specified by its icon name
+ * Selects a volume specified by its icon name.
  *
  * @param {Window} contentWindow Window to be tested.
  * @param {string} iconName Name of the volume icon.
@@ -255,6 +255,8 @@ test.util.sync.collapseSelectedFolderInTree = function(contentWindow) {
 /**
  * Fakes pressing the down arrow until the given |folderName| is selected in the
  * navigation tree.
+ * TODO(sashab): Merge this functionality into selectTeamDrive and remove this
+ * function.
  *
  * @param {Window} contentWindow Window to be tested.
  * @param {string} folderName Name of the folder to be selected.