Bug 1439974. Pass actual keypress events to the finder's keypress method, even in the e10s case. r=felipe

We could also, or in addition, pull the KeyboardEvent thing off the given
docshell in Finder.jsm and not rely on having these constants on the event
object we have.

I did look through the other places I changed in
https://hg.mozilla.org/mozilla-central/rev/b01bd36c3899 and the other ones that
get the constants off events look like they're EventListener instances, so
should have actual events coming via normal event dispatch.

toolkit/modules/RemoteFinder.jsm

@@ -209,6 +209,10 @@ function RemoteFinderListener(global) {
   this._finder = new Finder(global.docShell);
   this._finder.addResultListener(this);
   this._global = global;
+  this.KeyboardEvent =
+    global.docShell
+          .QueryInterface(Ci.nsIInterfaceRequestor)
+          .getInterface(Ci.nsIDOMWindow).KeyboardEvent;
 
   for (let msg of this.MESSAGES) {
     global.addMessageListener(msg, this);
@@ -314,7 +318,7 @@ RemoteFinderListener.prototype = {
         break;
 
       case "Finder:KeyPress":
-        this._finder.keyPress(data);
+        this._finder.keyPress(new this.KeyboardEvent("keypress", data));
         break;
 
       case "Finder:MatchesCount":