Revert "Disable newly flaky test MediaAppPreferredOverChromeApps"

This reverts commit 565b6fb9.

Reason for revert: Suspected real/root cause reverted in r774287

Original change's description:
> Disable newly flaky test MediaAppPreferredOverChromeApps
>
> Bug: 1090432
> Change-Id: I00eea4851b95669ffa5e6824d2eecf1366f65dbc
> Tbr: tapted@chromium.org
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2226972
> Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
> Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#774327}

TBR=dmazzoni@chromium.org,tapted@chromium.org

Change-Id: I24868bcd20d7089dd2bba158670a9c8dc12d1052
Bug: 1090432
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2228271
Commit-Queue: Trent Apted <tapted@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774518}

chrome/browser/chromeos/file_manager/file_tasks_browsertest.cc

@@ -417,9 +417,8 @@ IN_PROC_BROWSER_TEST_F(FileTasksBrowserTest, InstalledAppsAreImplicitDefaults) {
 
 // If the media app is enabled, it will be preferred over a chrome app with a
 // specific extension, unless that app is set default via prefs.
-// Flaky: http://crbug.com/1090432
 IN_PROC_BROWSER_TEST_F(FileTasksBrowserTestWithMediaApp,
-                       DISABLED_MediaAppPreferredOverChromeApps) {
+                       MediaAppPreferredOverChromeApps) {
   Profile* profile = browser()->profile();
   auto extension = InstallTiffHandlerChromeApp(profile);
   TestExpectationsAgainstDefaultTasks({{"tiff", kMediaAppId}});