Bug 1533462 - Execute the deferred font-info loader immediately when running reftests, to avoid intermittent issues due to async completion triggering an extra reflow mid-test. r=jwatt

Differential Revision: https://phabricator.services.mozilla.com/D87194

layout/reftests/font-matching/reftest.list

@@ -1,9 +1,3 @@
-# Run the font loader eagerly: this also ensures we will eagerly load localized
-# family names when looking up a requested font-family. Otherwise, tests here
-# may fail if they're running too soon after browser startup, and localized
-# names have not yet been read. (See bug 1439937.)
-defaults pref(gfx.font_loader.delay,0)
-
 == CSS21-t1502-no-inherited-font-family.xhtml CSS21-t1502-no-inherited-font-family-ref.xhtml
 
 # tests for bug 1394311 (case-insensitive lang tag processing)

layout/tools/reftest/runreftest.py

@@ -393,6 +393,10 @@ class RefTest(object):
         prefs['reftest.logLevel'] = options.log_tbpl_level or 'info'
         prefs['reftest.suite'] = options.suite
         prefs['gfx.font_rendering.ahem_antialias_none'] = True
+        # Run the "deferred" font-loader immediately, because if it finishes
+        # mid-test, the extra reflow that is triggered can disrupt the test.
+        prefs['gfx.font_loader.delay'] = 0
+        prefs['gfx.font_loader.interval'] = 0
         # Disable dark scrollbars because it's semi-transparent.
         prefs['widget.disable-dark-scrollbar'] = True
         prefs['reftest.isCoverageBuild'] = mozinfo.info.get('ccov', False)