Update base.js to fix race condition

In Chrome, the ObjectUrl was being revoked before the image fully loaded.  If you wrap that revoke into an onload handler for the image, it solves that problem.

html5demos/indexeddb/js/base.js

@@ -64,7 +64,9 @@
                 imgElephant.setAttribute("src", imgURL);
 
                 // Revoking ObjectURL
-                URL.revokeObjectURL(imgURL);
+                imgElephant.onload = function() {
+                    window.URL.revokeObjectURL(this.src);
+                }
             };
         };