Enable TheOnion on loading.desktop

These performance tests can re-enabled because the culprit
CL that caused these to fail (http://crrev.com/c/1423601)
has been reverted (in http://crrev.com/c/1457745). As a
result, the tests run fine now.

Bug: 928796
Change-Id: I771f53015448e42e019de0e94b2abb1811b932b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1557092
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649153}

tools/perf/expectations.config

@@ -86,8 +86,6 @@ crbug.com/876636 [ ChromeOS ] loading.desktop/TheOnion_cold [ Skip ]
 crbug.com/876636 [ ChromeOS ] loading.desktop/TheOnion_warm [ Skip ]
 crbug.com/876636 [ Win_10 ] loading.desktop/TheOnion_warm [ Skip ]
 crbug.com/876636 [ Win_7 ] loading.desktop/TheOnion_warm [ Skip ]
-crbug.com/928796 [ All ] loading.desktop/TheOnion_warm [ Skip ]
-crbug.com/928796 [ All ] loading.desktop/TheOnion_cold [ Skip ]
 crbug.com/876636 [ ChromeOS ] loading.desktop/AllRecipes_cold [ Skip ]
 crbug.com/876636 [ ChromeOS ] loading.desktop/AllRecipes_warm [ Skip ]
 crbug.com/879833 [ Mac_10.12 ] loading.desktop/AllRecipes_cold [ Skip ]