Bug 1510569 - Move Content:BrowserChildReady from WebProgressChild.jsm into the browser child frame script r=mconley

Differential Revision: https://phabricator.services.mozilla.com/D34565

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

toolkit/content/browser-child.js

@@ -15,6 +15,10 @@ docShell.QueryInterface(Ci.nsIInterfaceRequestor)
   .getInterface(Ci.nsIBrowserChild)
   .beginSendingWebProgressEventsToParent();
 
+// This message is used to measure content process startup performance in Talos
+// tests.
+sendAsyncMessage("Content:BrowserChildReady", { time: Services.telemetry.msSystemNow() });
+
 addEventListener("DOMTitleChanged", function(aEvent) {
   if (!aEvent.isTrusted || aEvent.target.defaultView != content)
     return;

toolkit/modules/WebProgressChild.jsm

@@ -34,9 +34,6 @@ class WebProgressChild {
     let webProgress = this.mm.docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                               .getInterface(Ci.nsIWebProgress);
     webProgress.addProgressListener(this._filter, notifyCode);
-
-    // This message is used for measuring this.mm.content process startup performance.
-    this.mm.sendAsyncMessage("Content:BrowserChildReady", { time: Services.telemetry.msSystemNow() });
   }
 
   _requestSpec(aRequest, aPropertyName) {