Bug 1550467 - Also install SimpleTest.is into the fission window. r=botond

I split this out so it's more obvious what pieces need to be modified
to add additional functions.

Differential Revision: https://phabricator.services.mozilla.com/D32188

--HG--
extra : moz-landing-system : lando

gfx/layers/apz/test/mochitest/FissionTestHelperChild.jsm

@@ -29,6 +29,8 @@ class FissionTestHelperChild extends JSWindowActorChild {
     let cw = this.cw();
     Cu.exportFunction((cond, msg) => this.sendAsyncMessage("ok", {cond, msg}),
                       cw, { defineAs: "ok" });
+    Cu.exportFunction((a, b, msg) => this.sendAsyncMessage("is", {a, b, msg}),
+                      cw, { defineAs: "is" });
 
     let FissionTestHelper = Cu.createObjectIn(cw, { defineAs: "FissionTestHelper" });
     FissionTestHelper.startTestPromise =

gfx/layers/apz/test/mochitest/FissionTestHelperParent.jsm

@@ -45,6 +45,10 @@ class FissionTestHelperParent extends JSWindowActorParent {
         FissionTestHelperParent.SimpleTest.ok(msg.data.cond, this.docURI() + " | " + msg.data.msg);
         break;
 
+      case "is":
+        FissionTestHelperParent.SimpleTest.is(msg.data.a, msg.data.b, this.docURI() + " | " + msg.data.msg);
+        break;
+
       case "Test:Complete":
         this._testCompletePromiseResolver();
         break;

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

@@ -29,7 +29,7 @@ async function* test() {
        .useRemoteSubframes,
      "OOP iframe is actually OOP");
   let iframeResult = await FissionTestHelper.sendToOopif(iframeElement, "20 + 22");
-  ok(iframeResult == 42, "Basic content fission test works");
+  is(iframeResult, 42, "Basic content fission test works");
 }
 
   </script>