Bug 1351008 - Lazily load Manifest jsms in manifestMessages.js. r=baku

This avoids loading 7 jsms until they are actually needed, reducing
content process memory usage.

MozReview-Commit-ID: 8ukNr7PL80A

--HG--
extra : rebase_source : a926a19645ffcacadec93ecc79927d356d603114

dom/ipc/manifestMessages.js

@@ -16,11 +16,16 @@
 const {
   utils: Cu,
 } = Components;
-Cu.import("resource://gre/modules/ManifestObtainer.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
-Cu.import("resource://gre/modules/ManifestFinder.jsm");
-Cu.import("resource://gre/modules/ManifestIcons.jsm");
 Cu.import("resource://gre/modules/Task.jsm");
 
+XPCOMUtils.defineLazyModuleGetter(this, "ManifestObtainer",
+				  "resource://gre/modules/ManifestObtainer.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ManifestFinder",
+				  "resource://gre/modules/ManifestFinder.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ManifestIcons",
+				  "resource://gre/modules/ManifestIcons.jsm");
+
 const MessageHandler = {
   registerListeners() {
     addMessageListener(