Disable DirectoryTree/FilesAppBrowserTest.Test/directoryTreeExpandHorizontalScrollRTL

Failin on linux-chromeos-chrome internal bot since
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/3955

Error like "[FAIL] [directoryTreeExpandHorizontalScrollRTL]: Tree should not scroll right

This is blocking src-internal rolls (for >1 day).

Tbr: majidvp@chromium.org, noel@chromium.org
Bug: 1061821, 1061670
Change-Id: I27dd3fca5a5d9154519680b748c6dd054f2dd021
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2103012Reviewed-by: Trent Apted <tapted@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750465}

chrome/browser/chromeos/file_manager/file_manager_browsertest.cc

@@ -531,7 +531,8 @@ WRAPPED_INSTANTIATE_TEST_SUITE_P(
         TestCase("directoryTreeRecentsSubtypeScroll").EnableUnifiedMediaView(),
         TestCase("directoryTreeHorizontalScroll"),
         TestCase("directoryTreeExpandHorizontalScroll"),
-        TestCase("directoryTreeExpandHorizontalScrollRTL"),
+        // Disabled. Fails on internal ChromeOS bot. https://crbug.com/1061821.
+        // TestCase("directoryTreeExpandHorizontalScrollRTL"),
         TestCase("directoryTreeVerticalScroll"),
         TestCase("directoryTreeExpandFolder")));