Merge SubframeLoader::createJavaAppletWidget into HTMLAppletElement::udpateWidget

This is its only callsite and the logic really should be part of HTMLAppletElement.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/20858002

git-svn-id: svn://svn.chromium.org/blink/trunk@155091 bbb929c8-8fbe-4397-9dbb-9b2b20218538