Use ICU for string pluralization in the extension permission dialog.

This adds support for using the correct plural form of a string for any
language. In particular, this uses the aforementioned support in the
extensions permission dialog for website access and retained file
access.

BUG=290046

Review URL: https://chromiumcodereview.appspot.com/23591040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224700 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224700