Make it possible to persist the disk and memory cache capacity prefs again.

Also, if the user doesn't have a disk cache parent folder chosen, show and
set the default which is the profile directory.
b=125189; r=morse; sr=sfraser

xpfe/components/prefwindow/resources/content/pref-cache.js

@@ -2,18 +2,51 @@
  *
  */
 
-const nsIFilePicker          = Components.interfaces.nsIFilePicker;
-const nsILocalFile           = Components.interfaces.nsILocalFile;
+const nsIFilePicker       = Components.interfaces.nsIFilePicker;
+const nsILocalFile        = Components.interfaces.nsILocalFile;
+const nsIFile             = Components.interfaces.nsIFile;
+const nsIProperties       = Components.interfaces.nsIProperties;
+const kCacheParentDirPref = "browser.cache.disk.parent_directory";
 
 function Startup()
 {
-  var pref = Components.classes["@mozilla.org/preferences-service;1"]
-                       .getService(Components.interfaces.nsIPrefBranch);
-  var path = Components.classes["@mozilla.org/file/local;1"]
-                       .createInstance(nsILocalFile);
-  
-  path =  pref.getComplexValue("browser.cache.disk.parent_directory", nsILocalFile);
-  document.getElementById("browserCacheDiskCacheFolder").value = path.unicodePath;
+  var path = null;
+  var pref = null;
+  try 
+  {
+    pref = Components.classes["@mozilla.org/preferences-service;1"]
+      .getService(Components.interfaces.nsIPrefBranch);
+    path = pref.getComplexValue(kCacheParentDirPref, nsILocalFile);
+  }
+  catch (ex)
+  {
+    // parent_directory pref not set; path is null so we'll failover
+    // to filling in the parent_directory as the profile directory
+  }
+
+  if (!path)
+  {
+    try
+    {
+      // no disk cache folder found; default to profile directory
+      var dirSvc = Components.classes["@mozilla.org/file/directory_service;1"]
+        .getService(nsIProperties);
+      var ifile = dirSvc.get("ProfD", nsIFile);
+      path = ifile.QueryInterface(nsILocalFile);
+
+      // now remember the new assumption
+      if (pref)
+        pref.setComplexValue(kCacheParentDirPref, nsILocalFile, path);
+    }
+    catch (ex)
+    {
+    }
+  }
+
+  // if both pref and dir svc fail leave this field blank else show path
+  if (path)
+    document.getElementById("browserCacheDiskCacheFolder").value = 
+      path.unicodePath;
 }
 
 
@@ -27,6 +60,16 @@ function prefCacheSelectFolder()
   var title = prefutilitiesBundle.getString("cachefolder");
 
   fp.init(window, title, nsIFilePicker.modeGetFolder);
+  try 
+  {
+    var initialDir = pref.getComplexValue(kCacheParentDirPref, nsILocalFile);
+    if (initialDir)
+      fp.displayDirectory = initialDir;
+  }
+  catch (ex)
+  {
+    // ignore exception: file picker will open at default location
+  }
   fp.appendFilters(nsIFilePicker.filterAll);
   var ret = fp.show();
 
@@ -35,7 +78,7 @@ function prefCacheSelectFolder()
     var viewable = fp.file.unicodePath;
     var folderField = document.getElementById("browserCacheDiskCacheFolder");
     folderField.value = viewable;
-    pref.setComplexValue("browser.cache.disk.parent_directory", nsILocalFile, localFile)
+    pref.setComplexValue(kCacheParentDirPref, nsILocalFile, localFile)
   }
 }