Fix 'except' and 'prefer' spelling.

content/test/data/dom_storage/sanity_check.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 function startTestSoon() {
   window.setTimeout(test, 0);
 }
 
 function test() {
   try {
@@ skipping 42 matching lines @@
              "storage['name'] != 'value' after addition");
 
   storage.clear();
 
   checkEqual(0, storage.length,
              "storage.length != 0 after clear");
 
   var tooLarge =  makeLargeString((5 * 1024 * 1024) + 1);
   try {
     storage.setItem("tooLarge", tooLarge);
-    throw "failed to throw execption for very large value";
+    throw "failed to throw exception for very large value";
   } catch(ex) {
     checkEqual(ex.code, 22,
                "ex.code != 22 for attempt to store a very large value");
   }
   try {
     storage.setItem(tooLarge, "key is too large");
-    throw "failed to throw execption for very large key";
+    throw "failed to throw exception for very large key";
   } catch(ex) {
     checkEqual(ex.code, 22,
                "ex.code != 22 for attempt to store a very large key");
   }
 }
 
 function checkEqual(lhs, rhs, errorMessage) {
   if (lhs !== rhs)
     throw errorMessage;
 }
 
 function makeLargeString(minimumSize) {
   return Array(minimumSize).join("X");
 }