Bug 1264231 - Part 4: add a TODO in test. r=kanru

As requested by Jonas, we should put a note in the test in case someone
would like to re-enable this in the future.

Right now the test will trigger the mismatch loadInfo and loadContext,
because it's using System Principal to fetch sub-resources, hence its
loadInfo doesn't have the isIsolatedMozBrowser flag set.

dom/inputmethod/mochitest/chrome.ini

@@ -37,7 +37,7 @@ disabled = fails because receiving bad values
 [test_bug1137557.html]
 [test_bug1175399.html]
 [test_focus_blur_manage_events.html]
-disabled = fails because receiving bad events
+disabled = fails because receiving bad events # also depends on bug 1254823
 [test_forward_hardware_key_to_ime.html]
 skip-if = buildapp != 'mulet'
 [test_input_registry_events.html]