Bug 632170 - Use updates directory environmental variable [r=mfinkle, a=blockin-fennec]

mobile/components/DirectoryProvider.js

@@ -45,6 +45,7 @@ Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
 
 const NS_APP_CACHE_PARENT_DIR = "cachePDir";
 const XRE_UPDATE_ROOT_DIR     = "UpdRootD";
+const ENVVAR_UPDATE_DIR       = "UPDATES_DIRECTORY";
 
 function DirectoryProvider() {}
 
@@ -74,6 +75,15 @@ DirectoryProvider.prototype = {
           return profile;
       }
     } else if (prop == XRE_UPDATE_ROOT_DIR) {
+      let env = Cc["@mozilla.org/process/environment;1"].getService(Ci.nsIEnvironment);
+      if (env.exists(ENVVAR_UPDATE_DIR)) {
+        let path = env.get(ENVVAR_UPDATE_DIR);
+        if (path) {
+          let localFile = Cc["@mozilla.org/file/local;1"].createInstance(Ci.nsILocalFile);
+          localFile.initWithPath(path);
+          return localFile;
+        }
+      }
       let dm = Cc["@mozilla.org/download-manager;1"].getService(Ci.nsIDownloadManager);
       return dm.defaultDownloadsDirectory;
     }