Files app: Force some tests to run with FilesNg disabled

Force some tests to run without FilesNg because they depend on the
breadcrumb and the new breadcrumb isn't 100% ready:

 - tabindex*
 - breadcrumbsNavigate
 - breadcrumbsLeafNoFocus
 - showMyFiles

Other tests disabled for FilesNg were due to name conflicting when using
EnableFilesNg() and without it, both getting the suffix _FilesNg, forced
DisableFilesNg() to make it explicit and have no suffix.

Bug: 992818
Change-Id: I3737dfdb5bcd46f5fd6952fc38346880950c86e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2087880Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Auto-Submit: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747129}

chrome/browser/chromeos/file_manager/file_manager_browsertest_base.cc

@@ -1342,6 +1342,8 @@ void FileManagerBrowserTestBase::SetUpCommandLine(
 
   if (IsFilesNgTest()) {
     enabled_features.emplace_back(chromeos::features::kFilesNG);
+  } else {
+    disabled_features.emplace_back(chromeos::features::kFilesNG);
   }
 
   if (IsArcTest()) {