use session storage for stats cache (bug 701696)

media/js/impala/stats/manager.js

@@ -11,11 +11,11 @@ z.StatsManager = (function() {
 
     // The version of the stats localStorage we are using.
     // If you increment this number, you cache-bust everyone!
-    var STATS_VERSION = '2011-10-21-1';
+    var STATS_VERSION = '2011-12-12';
     var PRECISION = 2;
 
     var storage         = z.Storage("stats"),
-        storageCache    = z.Storage("statscache"),
+        storageCache    = z.SessionStorage("statscache"),
         dataStore       = {},
         currentView     = {},
         addonId         = parseInt($(".primary").attr("data-addon_id"), 10),

media/js/zamboni/storage.js

@@ -44,3 +44,32 @@ z.Storage = (function() {
         };
     };
 })();
+
+z.SessionStorage = (function() {
+    var cookieStorage = {
+        getItem: function(key) {
+            return $.cookie(key);
+        },
+        setItem: function(key, value) {
+            return $.cookie(key, value, {path: '/'});
+        },
+        removeItem: function(key) {
+            return $.cookie(key, null);
+        }
+    };
+    var engine = z.capabilities.localStorage ? sessionStorage : cookieStorage;
+    return function(namespace) {
+        namespace = namespace ? namespace + '-' : '';
+        return {
+            get: function(key) {
+                return engine.getItem(namespace + key);
+            },
+            set: function(key, value) {
+                return engine.setItem(namespace + key, value);
+            },
+            remove: function(key) {
+                return engine.removeItem(namespace + key);
+            }
+        };
+    };
+})();