Delete the extensions i18n message map when extension unload is received.

chrome/test/data/extensions/api_test/i18nUpdate/contentscript.js

Index: chrome/test/data/extensions/api_test/i18nUpdate/contentscript.js
diff --git a/chrome/test/data/extensions/activity_log/google_cs.js b/chrome/test/data/extensions/api_test/i18nUpdate/contentscript.js
similarity index 67%
copy from chrome/test/data/extensions/activity_log/google_cs.js
copy to chrome/test/data/extensions/api_test/i18nUpdate/contentscript.js
index acd9bbb813b86c126c3cb640ec5acf47aab528c1..8cbfc7c0e1ee51c74e9ee03646686000608eb1be 100644
--- a/chrome/test/data/extensions/activity_log/google_cs.js
+++ b/chrome/test/data/extensions/api_test/i18nUpdate/contentscript.js
@@ -2,4 +2,5 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-document.write("g o o g l e");
+document.title = chrome.i18n.getMessage("testMessage");
+chrome.test.notifyPass();