Enable PrerenderTests on Android.

Looks like they haven't been enabled since before Android
was upstreamed to the public repo.

BUG=138275

Review-Url: https://codereview.chromium.org/2197333002
Cr-Original-Commit-Position: refs/heads/master@{#409182}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 50ec2e97b08adc6f322a49a73cc12f8063242c1c

android/pylib/gtest/filter/unit_tests_disabled

@@ -86,9 +86,6 @@ ProfileSyncComponentsFactoryImplTest.*
 PermissionsTest.GetWarningMessages_Plugins
 ImageOperations.ResizeShouldAverageColors
 
-# crbug.com/138275
-PrerenderTest.*
-
 # crbug.com/139643
 VariationsUtilTest.DisableAfterInitialization
 VariationsUtilTest.AssociateGoogleVariationID