Added 16x16 icon required by Web Store.

BUG=none
TEST=Only a problem when uploading to the Web Store.
Review URL: http://codereview.chromium.org/4347002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@64864 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/chat_manager/manifest.json

@@ -4,6 +4,7 @@
   "version": "1.0.16",
   "icons": {
     "128": "128.png",
+    "16": "16.png",
     "24": "24.png",
     "32": "32.png",
     "48": "48.png"