Bug 1470280 - Part 2: Just use osPid to check for new process. r=mconley

The 'ipc:content-created' topic doesn't always seem to be propagated to the
browser_force_process_selector.js test. It appears it's not necessary to
actually wait for it, so lets just remove that.

--HG--
extra : rebase_source : 442a64ff580a8c26bca93723d24128184c5798d6
extra : source : fe7ccd9fee7621782676d9bd841c144126e24c04

dom/base/test/browser_force_process_selector.js

@@ -5,14 +5,11 @@ const CONTENT_CREATED = "ipc:content-created";
 // Make sure that BTU.withNewTab({ ..., forceNewProcess: true }) loads
 // new tabs in their own process.
 async function spawnNewAndTest(recur, pids) {
-  let processCreated = TestUtils.topicObserved(CONTENT_CREATED);
   await BrowserTestUtils.withNewTab({ gBrowser, url: "about:blank", forceNewProcess: true },
                                     async function(browser) {
-      // Make sure our new browser is in its own process. The processCreated
-      // promise should have already resolved by this point.
-      await processCreated;
+      // Make sure our new browser is in its own process.
       let newPid = browser.frameLoader.tabParent.osPid;
-      ok(!pids.has(newPid), "new tab is in its own process");
+      ok(!pids.has(newPid), "new tab is in its own process: " + recur);
       pids.add(newPid);
 
       if (recur) {