Bug 1473004: Don't attempt to guess a favicon in performance tests. r=jmaher

Favicons will cause a small bit of additional network traffic and work in the
content process for any loaded page that doesn't specify a favicon. This turns
off attempts to guess a favicon when one isn't specified in performance tests.

Differential Revision: https://phabricator.services.mozilla.com/D1936

--HG--
extra : moz-landing-system : lando

testing/profiles/common/user.js

@@ -1,6 +1,7 @@
 // Base preferences file used by both unittest and perf harnesses.
 /* globals user_pref */
 user_pref("app.update.enabled", false);
+user_pref("browser.chrome.guess_favicon", false);
 user_pref("browser.dom.window.dump.enabled", true);
 // Use an empty list of sites to avoid fetching
 user_pref("browser.newtabpage.activity-stream.feeds.section.topstories", false);

testing/profiles/unittest/user.js

@@ -15,7 +15,6 @@ user_pref("app.update.url.android", "");
 // bug 1210465.
 user_pref("apz.content_response_timeout", 60000);
 user_pref("browser.EULA.override", true);
-user_pref("browser.chrome.guess_favicon", false);
 // Make sure we don't try to load snippets from the network.
 user_pref("browser.aboutHomeSnippets.updateUrl", "nonexistent://test");
 // Disable Bookmark backups by default.