Set viewport size for autoscale tests

We were incorrectly relying on the viewport being indirectly set
for us. Make sure we are explicit in what we want for these tests.

tests/test.display.js

@@ -223,6 +223,7 @@ describe('Display/Canvas Helper', function () {
             display = new Display(canvas);
             display.clipViewport = true;
             display.resize(4, 3);
+            display.viewportChangeSize(4, 3);
             document.body.appendChild(canvas);
         });