Made WebKit notifications display 80x80 icons if they have them.

In the rich notification center and toasts, WebKit notifications
(those created with webkitNotifications.createNotification() or with
chrome.notifications.create({type: "simple"})) usually display their
icons in a 40x40 square, as that was the size used for notification
icons before rich notifications.

This code change causes icons that are exacly 80x80 pixels and that have
no transparency to be displayed using the full 80x80 pixel space
available with rich notifications. This allows developers to create
notifications from web pages and from apps that need to work without
rich notifications that will look as as good as they can with rich
notifications.
    
BUG=222175
R=mukai@chromium.org
TBR=pkotwicz@chromium.org

Review URL: https://chromiumcodereview.appspot.com/12879009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194026 0039d316-1c4b-4281-b951-d872f2087c98