Add NPAPI deprecation message to extensions docs.

BUG=295137
NOTRY=true

Review URL: https://codereview.chromium.org/25760002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226488 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/docs/templates/articles/npapi.html

@@ -11,6 +11,9 @@ allowing you to call into native binary code from JavaScript.
 
 <h2 id="warning">Warning</h2>
 
+<p align="center"><b><a href="http://blog.chromium.org/2013/09/saying-goodbye-to-our-old-friend-npapi.html">NPAPI is being phased out.</a>
+Consider using alternatives.</b></p>
+
 <p align="center"><b>NPAPI is a really big hammer that should only be used when no other approach will work.</b>
 
 <p>Code running in an NPAPI plugin has the full permissions of the current user and is not sandboxed or shielded from malicious input by Google Chrome in any way. You should be especially cautious when processing input from untrusted sources, such as when working with <a href="content_scripts.html#security-considerations">content scripts</a> or XMLHttpRequest.