Don't force reload from cache on form resubmission via reload.

If we set a cache policy of ReturnCacheDataDontLoad on a form submission reload, we generate a form submission warning, but if the user chooses to continue, we ignore that and just load from the cache instead of resubmitting.

By changing to a forced reload, we cancel if the user cancels and resubmit if the user asks for it.

BUG=263508

Review URL: https://chromiumcodereview.appspot.com/23444047

git-svn-id: svn://svn.chromium.org/blink/trunk@157587 bbb929c8-8fbe-4397-9dbb-9b2b20218538