Bug 1412049 - Clear filterbar visible prefs between tests; r=Honza.

This was making browser_webconsole_filters.js fail on verify mode, and
could potentially cause other issues in the future.

MozReview-Commit-ID: 9syLDYAjm6S

--HG--
extra : rebase_source : 67b4645834f0700c52da7355e4834f8da308515e

devtools/client/webconsole/new-console-output/test/mochitest/head.js

@@ -21,6 +21,7 @@ var WCUL10n = require("devtools/client/webconsole/webconsole-l10n");
 Services.prefs.setBoolPref("devtools.webconsole.new-frontend-enabled", true);
 registerCleanupFunction(function* () {
   Services.prefs.clearUserPref("devtools.webconsole.new-frontend-enabled");
+  Services.prefs.clearUserPref("devtools.webconsole.ui.filterbar");
 
   // Reset all filter prefs between tests. First flushPrefEnv in case one of the
   // filter prefs has been pushed for the test