Bug 1171013 - Extend defineLazyModuleGetter to support user-defined proxy objects. r=mfinkle

dom/apps/Webapps.jsm

@@ -203,6 +203,7 @@ this.DOMApplicationRegistry = {
   dirKey: DIRECTORY_NAME,
 
   init: function() {
+    // Keep the messages in sync with the lazy-loading in browser.js (bug 1171013).
     this.messages = ["Webapps:Install",
                      "Webapps:Uninstall",
                      "Webapps:GetSelf",

js/xpconnect/loader/XPCOMUtils.jsm

@@ -231,7 +231,9 @@ this.XPCOMUtils = {
 
   /**
    * Defines a getter on a specified object for a module.  The module will not
-   * be imported until first use.
+   * be imported until first use. The getter allows to execute setup and
+   * teardown code (e.g.  to register/unregister to services) and accepts
+   * a proxy object which acts on behalf of the module until it is imported.
    *
    * @param aObject
    *        The object to define the lazy getter on.
@@ -242,15 +244,35 @@ this.XPCOMUtils = {
    * @param aSymbol
    *        The name of the symbol exported by the module.
    *        This parameter is optional and defaults to aName.
+   * @param aPreLambda
+   *        A function that is executed when the proxy is set up.
+   *        This will only ever be called once.
+   * @param aPostLambda
+   *        A function that is executed when the module has been imported to
+   *        run optional teardown procedures on the proxy object.
+   *        This will only ever be called once.
+   * @param aProxy
+   *        An object which acts on behalf of the module to be imported until
+   *        the module has been imported.
    */
-  defineLazyModuleGetter: function XPCU_defineLazyModuleGetter(aObject, aName,
-                                                               aResource,
-                                                               aSymbol)
+  defineLazyModuleGetter: function XPCU_defineLazyModuleGetter(
+                                   aObject, aName, aResource, aSymbol,
+                                   aPreLambda, aPostLambda, aProxy)
   {
+    let proxy = aProxy || {};
+
+    if (typeof(aPreLambda) === "function") {
+      aPreLambda.apply(proxy);
+    }
+
     this.defineLazyGetter(aObject, aName, function XPCU_moduleLambda() {
       var temp = {};
       try {
         Cu.import(aResource, temp);
+
+        if (typeof(aPostLambda) === "function") {
+          aPostLambda.apply(proxy);
+        }
       } catch (ex) {
         Cu.reportError("Failed to load module " + aResource + ".");
         throw ex;