Revert "Sheriff: Disable Flaky FilesAppBrowserTests in TabletMode."

This reverts commit b988cfa5.

Reason for revert: per https://crbug.com/1102947#c4, this was already fixed a day earlier, in https://crbug.com/1100152

Original change's description:
> Sheriff: Disable Flaky FilesAppBrowserTests in TabletMode.
> 
> Flaky tests include: (FileDisplay|QuickView)/FilesAppBrowserTest.Test/(fileDisplayDrive|openQuickView|fileDisplayDownloads)_TabletMode.
> 
> Flake occurrences can be viewed at https://analysis.chromium.org/p/chromium/flake-portal/flakes/occurrences?key=ag9zfmZpbmRpdC1mb3ItbWVyOgsSBUZsYWtlIi9jaHJvbWl1bUBicm93c2VyX3Rlc3RzQEZpbGVzQXBwQnJvd3NlclRlc3QuVGVzdAw
> 
> TBR: lucmult@chromium.org
> Bug: 1102947
> Change-Id: Id39ff39a94e955f0a513b7e5ddceef264846beae
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2285298
> Reviewed-by: Darwin Huang <huangdarwin@chromium.org>
> Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#786050}

TBR=lucmult@chromium.org,huangdarwin@chromium.org

Change-Id: I5cb75418c2be74a1ad4dda713376ece9e66de164
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1102947
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2286190Reviewed-by: Darwin Huang <huangdarwin@chromium.org>
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786085}

chrome/browser/chromeos/file_manager/file_manager_browsertest.cc

@@ -40,7 +40,6 @@ struct TestCase {
     return *this;
   }
 
-  // Note: All TabletMode tests are currently disabled (crbug.com/1102947).
   TestCase& TabletMode() {
     options.tablet_mode = true;
     return *this;
@@ -234,12 +233,10 @@ WRAPPED_INSTANTIATE_TEST_SUITE_P(
     ::testing::Values(
         TestCase("fileDisplayDownloads"),
         TestCase("fileDisplayDownloads").InGuestMode(),
-        // Disabled flaky test (crbug.com/1102947)
-        // TestCase("fileDisplayDownloads").TabletMode(),
+        TestCase("fileDisplayDownloads").TabletMode(),
         TestCase("fileDisplayLaunchOnLocalFolder").DontObserveFileTasks(),
         TestCase("fileDisplayLaunchOnDrive").DontObserveFileTasks(),
-        // Disabled flaky test (crbug.com/1102947)
-        // TestCase("fileDisplayDrive").TabletMode(),
+        TestCase("fileDisplayDrive").TabletMode(),
         TestCase("fileDisplayDrive"),
         TestCase("fileDisplayDriveOffline").Offline(),
         TestCase("fileDisplayDriveOnline"),
@@ -450,8 +447,7 @@ WRAPPED_INSTANTIATE_TEST_SUITE_P(
         TestCase("openQuickViewDialog"),
         TestCase("openQuickViewAndEscape"),
         TestCase("openQuickView").InGuestMode(),
-        // Disabled flaky test (crbug.com/1102947)
-        // TestCase("openQuickView").TabletMode(),
+        TestCase("openQuickView").TabletMode(),
         TestCase("openQuickViewViaContextMenuSingleSelection"),
         TestCase("openQuickViewViaContextMenuCheckSelections"),
         TestCase("openQuickViewAudio"),