Revert "Disabled tests in chromeos dbg due to flakiness."

This reverts commit d8fb3e8f.

Reason for revert: No evidence of flake on flakiness dashboard for
these tests in DEBUG, yet find.it said there was. Who's right?

Well, reverting this CL to find.it out (the cause was a bad v8 roll
by the looks).

Original change's description:
> Disabled tests in chromeos dbg due to flakiness.
>
> Only one of the subtests reported flaky, but didn't know how to disable
> them separately.
>
> TBR=noel@chromium.org
>
> Bug: 871684
> Change-Id: Ie4f27cc5681ba3c6174853dbbfd16d1ba665c451
> Reviewed-on: https://chromium-review.googlesource.com/1164958
> Reviewed-by: Rune Lillesveen <futhark@chromium.org>
> Commit-Queue: Rune Lillesveen <futhark@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#581194}

TBR=futhark@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 871684
No-try: true
No-presubmit: true
Change-Id: Ibf9f9ee10ac3e1d37fb13c6b69ddac56071747a9
Reviewed-on: https://chromium-review.googlesource.com/1168842
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581803}

chrome/browser/chromeos/file_manager/file_manager_browsertest.cc

@@ -245,14 +245,8 @@ WRAPPED_INSTANTIATE_TEST_CASE_P(
                       TestCase("createFolderDrive"),
                       TestCase("createFolderDrive").EnableDriveFs()));
 
-// crbug.com/871684
-#if !defined(NDEBUG)
-#define MAYBE_KeyboardOperations DISABLED_KeyboardOperations
-#else
-#define MAYBE_KeyboardOperations KeyboardOperations
-#endif
 WRAPPED_INSTANTIATE_TEST_CASE_P(
-    MAYBE_KeyboardOperations, /* keyboard_operations.js */
+    KeyboardOperations, /* keyboard_operations.js */
     FilesAppBrowserTest,
     ::testing::Values(TestCase("keyboardDeleteDownloads").InGuestMode(),
                       TestCase("keyboardDeleteDownloads"),