Bug 836045 - Update Webapps code to use the new deviceStorage stat() support r=djf

dom/apps/src/FreeSpaceWatcher.jsm

@@ -44,13 +44,13 @@ this.FreeSpaceWatcher = {
         try {
           let deviceStorage = Services.wm.getMostRecentWindow("navigator:browser")
                                          .navigator.getDeviceStorage("apps");
-          let req = deviceStorage.stat();
+          let req = deviceStorage.freeSpace();
           req.onsuccess = req.onerror = function statResult(e) {
             if (!e.target.result) {
               return;
             }
 
-            let freeBytes = e.target.result.freeBytes;
+            let freeBytes = e.target.result;
             debug("Free bytes: " + freeBytes);
             let newStatus = freeBytes > aThreshold;
             if (newStatus != callback.currentStatus) {

dom/apps/src/Webapps.jsm

@@ -2265,7 +2265,7 @@ this.DOMApplicationRegistry = {
 
     let deviceStorage = Services.wm.getMostRecentWindow("navigator:browser")
                                 .navigator.getDeviceStorage("apps");
-    let req = deviceStorage.stat();
+    let req = deviceStorage.freeSpace();
     req.onsuccess = req.onerror = function statResult(e) {
       // Even if we could not retrieve the device storage free space, we try
       // to download the package.
@@ -2274,7 +2274,7 @@ this.DOMApplicationRegistry = {
         return;
       }
 
-      let freeBytes = e.target.result.freeBytes;
+      let freeBytes = e.target.result;
       if (freeBytes) {
         debug("Free storage: " + freeBytes + ". Download size: " +
               aApp.downloadSize);