HTMLFormControlElementWithState::shouldSaveAndRestoreFormControlState should not use confusingAndOftenMisusedAttached()

This code is used when restoring and saving form control state in the
history controller and when parsing. What it was really trying to check
was that the elements are in an active document so change the call to
inActiveDocument().

Review URL: https://codereview.chromium.org/51053002

git-svn-id: svn://svn.chromium.org/blink/trunk@160876 bbb929c8-8fbe-4397-9dbb-9b2b20218538