[mathml] Use Ahem font in mathml/relations/css-styling/display-2.html

That way we ensure that the font is the same in all platforms,
and we just need a generic -expected.txt file.

Change-Id: Ia5751e5de15c007619968f47f7015df49480d049

mathml/relations/css-styling/display-2.html

@@ -9,6 +9,7 @@
 <script src="/resources/testharnessreport.js"></script>
 <script src="/mathml/support/layout-comparison.js"></script>
 <script src="/mathml/support/mathml-fragments.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
 <style>
   mfrac {
       padding: 0;
@@ -97,7 +98,7 @@
   };
 
   setup({ explicit_done: true });
-  window.addEventListener("load", runTests);
+  document.fonts.ready.then(() => { runTests(); })
 
   function runTests() {
 
@@ -108,7 +109,7 @@
               replace(/X/g, `<mspace style="display: inline-block; width: ${Xsize}px; height: ${Xsize}px; background: black"></mspace>`);
           let reference = mathtest.
               replace(/maction|math|mfrac|mmultiscripts|mover|mover|mpadded|mrow|mspace|msubsup|msub|msup|mtable|munderover|munder/g, "div");
-          document.body.insertAdjacentHTML("beforeend", `<div style="position: absolute;">\
+          document.body.insertAdjacentHTML("beforeend", `<div style="font: 20px/1 Ahem; position: absolute;">\
 <div><span>${key}:</span>${mathtest}</div>\
 <div><span>${key}:</span>${reference}</div>\
 </div>`);