Reload after pushState or replaceState should always be a GET.

Accomplish this by reloading using data from the current history item, rather
than from DocumentLoader::request().

BUG=239907
TEST=http/tests/history/post-replace-state-reload.html

Review URL: https://codereview.chromium.org/165023002

git-svn-id: svn://svn.chromium.org/blink/trunk@167216 bbb929c8-8fbe-4397-9dbb-9b2b20218538