FrameLoader::reload should not use provisional loaders.

Reloading provisional loaders doesn't match other browser behavior or our own
and causes problems with re-submitting POSTs.  It also results in clobbering
entries in the history, though that may be a more recent regression.

This effectively reverts
https://chromiumcodereview.appspot.com/15288006
To avoid completely regressing the Android bug, as well as reloads on
session restore, also fix WebFrame::currentHistoryItem() to only
return the current history item, rather than also the provisional one.
(See comment #12 on bug.)

BUG=324308
TEST=WebFrameTest.ReloadWhileProvisional
     WebFrameTest.CurrentHistoryItem
     Load https://davidben.net/sleep-10s.py, restart browser, press Ctrl-R as page is restoring. Should not go to about:blank.

Review URL: https://codereview.chromium.org/99583005

git-svn-id: svn://svn.chromium.org/blink/trunk@164248 bbb929c8-8fbe-4397-9dbb-9b2b20218538