Bug 1384232: Same for test_xultree_animation.xhtml. r=me

MozReview-Commit-ID: HFo0aFXezzF

image/test/mochitest/test_xultree_animation.xhtml

@@ -52,7 +52,7 @@ Mozilla Bug 666446: lots of animated gifs swamp us with paint events
 
 if (SpecialPowers.DOMWindowUtils.isStyledByServo) {
   // Stylo currently asserts for any XUL bits.
-  SimpleTest.expectAssertions(9, 9);
+  SimpleTest.expectAssertions(7, 7);
 }
 
 const FAILURE_TIMEOUT = 5000; // Fail early after 120 seconds (2 minutes)