Fix for http://bugs.webkit.org/show_bug.cgi?id=13630
        and
        <rdar://problem/4873628>

        Back/Forward cache should work with pages with login fields.

        First change is to relocate the "useSecureKeyboardEntry" flag to the document.  This lets
        it persist through page cache transitions and it is truly a per-document concept more than
        per-frame anyways since its the document that has a password field, not the frame.

        Second change is to introduce the concept of an Element getting a "didRestoreFromCache()" callback.
        The idea is for elements to register with the document if they need work to be done when the
        page comes out of the back/forward cache.  Currently the only client of this service is 
        HTMLInputElements that are input type == PASSWORD.  Such an element's implementation for this
        method is to call reset()

        Finally, after a page is restored from the cache we have the document send the didRestoreFromCache()
        callback to its registered Elements.  The whole design is to clear the password fields after 
        restoring the page instead of when caching the page because we want to defer work for the common
        case - there shouldn't be extra work here just to navigate away from a page when the common case
        is that you'll never go back!

        No layout tests possible until http://bugs.webkit.org/show_bug.cgi?id=13672 is resolved

        * dom/Document.cpp:
        (WebCore::Document::Document):
        (WebCore::Document::registerForDidRestoreFromCacheCallback): Add an Element to the special page-restoration callback list
        (WebCore::Document::unregisterForDidRestoreFromCacheCallback): Remove such an element
        (WebCore::Document::didRestoreFromCache): Called by FrameLoader - dispatch to all the registered elements
        (WebCore::Document::setUseSecureKeyboardEntryWhenActive): Set the local flag and call updateSecureKeyboardEntryIfActive
          on the Frame
        (WebCore::Document::useSecureKeyboardEntryWhenActive): Return the flag

        * dom/Document.h:
        (WebCore::Document::unregisterFormElementWithState): Renamed

        * dom/Element.h:
        (WebCore::Element::didRestoreFromCache): Added virtual base method

        * html/HTMLInputElement.cpp:
        (WebCore::HTMLInputElement::~HTMLInputElement): Deregister from the document if inputType == PASSWORD
        (WebCore::HTMLInputElement::dispatchFocusEvent): Set the flag on the document, not the frame
        (WebCore::HTMLInputElement::dispatchBlurEvent): Ditto
        (WebCore::HTMLInputElement::setInputType): If changing to/from PASSWORD, register/deregister in the document accordingly
        (WebCore::HTMLInputElement::attach): Call registerForDidRestoreFromCacheCallback(this) instead of passwordFieldAdded()
        (WebCore::HTMLInputElement::didRestoreFromCache): Call reset();
        * html/HTMLInputElement.h:

        * html/HTMLSelectElement.cpp:
        (WebCore::HTMLSelectElement::~HTMLSelectElement): Renamed deregisterFormElementWithState to unregisterFormElementWithState
        * html/HTMLTextAreaElement.cpp:
        (WebCore::HTMLTextAreaElement::~HTMLTextAreaElement): Ditto

        * loader/FrameLoader.cpp:
        (WebCore::FrameLoader::canCachePage): Remove the check for password fields - they're allowed now!
        (WebCore::FrameLoader::opened): Tell the document to dispatch to the registered elements
        (WebCore::FrameLoader::saveDocumentState): Remove the check for password fields.  Turns out that when we grab a copy a the
          form state we're only copying the state of form elements that are registered with the Document - and that set 
          explicitly excludes Password elements

        * page/Frame.cpp:
        (WebCore::Frame::setDocument): If the frame is active, set the setUseSecureKeyboardEntry based on the setting contained
          in the new document
        (WebCore::Frame::updateSecureKeyboardEntryIfActive): Notification for the secure entry flag changing - if the Frame is
          active, then update to the new setting from the document
        (WebCore::Frame::setIsActive): Grab the useSecureKeyboardEntry flag from the document instead of FramePrivate
        (WebCore::FramePrivate::FramePrivate):
        * page/Frame.h:
        * page/FramePrivate.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@21430 268f45cc-cd09-0410-ab3c-d52691b4dbfc