Re-land: Re-enable TabindexFocusDownloads/FileManagerBrowserTest

Enabled in RELEASE, now re-enable this test in DEBUG/MSAN/ASAN.

Re-land. Was reverted on crrev.com/558004. Actual problem was an ASAN
flake [1] and every subsequent run of this test was green on the ASAN
bots before the revert landed (see image crbug.com/836254#c43).

[1] ASAN flake crbug.com/837950

Tbr: slangley, fukino
Bug: 836254
Change-Id: I1f1e60ad80130c5f2d7d92131fe21257f4ffa001
Reviewed-on: https://chromium-review.googlesource.com/1056507Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558110}

chrome/browser/chromeos/file_manager/file_manager_browsertest.cc

@@ -360,13 +360,8 @@ WRAPPED_INSTANTIATE_TEST_CASE_P(
     FileManagerBrowserTestWithLegacyEventDispatch,
     ::testing::Values(TestParameter(NOT_IN_GUEST_MODE, "tabindexFocus")));
 
-#if defined(DISABLE_SLOW_FILESAPP_TESTS)
-#define MAYBE_TabindexFocusDownloads DISABLED_TabindexFocusDownloads
-#else
-#define MAYBE_TabindexFocusDownloads TabindexFocusDownloads
-#endif
 WRAPPED_INSTANTIATE_TEST_CASE_P(
-    MAYBE_TabindexFocusDownloads,
+    TabindexFocusDownloads,
     FileManagerBrowserTestWithLegacyEventDispatch,
     ::testing::Values(TestParameter(NOT_IN_GUEST_MODE,
                                     "tabindexFocusDownloads"),