Bug 571902 - Land sync and crypto components on trunk [r=mconnor]

If resource://services-sync isn't defined yet, alias it to resource://gre/modules/services-sync.

services/sync/Weave.js

@@ -56,6 +56,7 @@ WeaveService.prototype = {
       let os = Cc["@mozilla.org/observer-service;1"].
         getService(Ci.nsIObserverService);
       os.addObserver(this, "final-ui-startup", true);
+      this.addResourceAlias();
       break;
 
     case "final-ui-startup":
@@ -68,6 +69,26 @@ WeaveService.prototype = {
       }, 10000, Ci.nsITimer.TYPE_ONE_SHOT);
       break;
     }
+  },
+
+  addResourceAlias: function() {
+    let ioService = Cc["@mozilla.org/network/io-service;1"]
+                    .getService(Ci.nsIIOService);
+    let resProt = ioService.getProtocolHandler("resource")
+                  .QueryInterface(Ci.nsIResProtocolHandler);
+
+
+    // Only create alias if resource://services-sync doesn't already exist.
+    if (resProt.hasSubstitution("services-sync"))
+      return;
+
+    let uri = ioService.newURI("resource://gre/modules/services-sync",
+                               null, null);
+    let file = uri.QueryInterface(Ci.nsIFileURL)
+               .file.QueryInterface(Ci.nsILocalFile);
+
+    let aliasURI = ioService.newFileURI(file);
+    resProt.setSubstitution("services-sync", aliasURI);
   }
 };