Bug 1263416 - Disable displayport expiry for test_basic_pan.html. r=botond

MozReview-Commit-ID: BIUv3JnDtKQ

--HG--
extra : rebase_source : c9518d8dbd3b0325984e36eeb3af9bf597de68f1

gfx/layers/apz/test/mochitest/test_basic_pan.html

@@ -60,6 +60,11 @@ window.onload = function() {
         // want those pans to turn into fling animations, so we increase the
         // fling-stop threshold velocity to absurdly high.
         ["apz.fling_stopped_threshold", "10000"],
+        // The helper_div_pan's div gets a displayport on scroll, but if the
+        // test takes too long the displayport can expire before the new scroll
+        // position is synced back to the main thread. So we disable displayport
+        // expiry for these tests.
+        ["apz.displayport_expiry_ms", 0],
       ]
     }, testDone);
 };