Bug 891840 - Re-enable test_pixel_lengths.html now that the underlying platform bug has been fixed. r=me

--HG--
extra : rebase_source : 896d2b1f078ade77d5d99b6f2b00759242d0eb34

layout/style/test/mochitest.ini

@@ -170,7 +170,6 @@ skip-if = (toolkit == 'gonk' && debug) || android_version == '10' #debug-only fa
 [test_parse_url.html]
 [test_parser_diagnostics_unprintables.html]
 [test_pixel_lengths.html]
-skip-if = true # bug 891840 - intermittent crashes
 [test_pointer-events.html]
 [test_position_sticky.html]
 support-files = file_position_sticky.html