<rdar://problem/8837307>, <rdar://problem/8637038>, and https://bugs.webkit.org/show_bug.cgi?id=52248
Back/forward list recovery after a WebProcess crash is crashy itself.

Reviewed by Sam Weinig.

Add an isEmpty() accessor so the WebProcess knows if it is actually restoring a session:
* Shared/SessionState.cpp:
(WebKit::SessionState::isEmpty):
* Shared/SessionState.h:

Keep track of the highest used itemID so a relaunched WebProcess can later be informed:
* Shared/WebBackForwardListItem.cpp:
(WebKit::WebBackForwardListItem::WebBackForwardListItem):
(WebKit::WebBackForwardListItem::highedUsedItemID):
* Shared/WebBackForwardListItem.h:
* WebProcess/WebPage/WebBackForwardListProxy.cpp:
(WebKit::generateHistoryItemID):
(WebKit::WebBackForwardListProxy::setHighestItemIDFromUIProcess):
(WebKit::WebBackForwardListProxy::addItemFromUIProcess): Remove a now-invalid ASSERT, as the UIProcess
  now tells the WebProcess that a previous WebProcess created.
* WebProcess/WebPage/WebBackForwardListProxy.h:

Encode/decode data relevant to restoring a session on WebPage creation:
* Shared/WebPageCreationParameters.cpp:
(WebKit::WebPageCreationParameters::encode):
(WebKit::WebPageCreationParameters::decode):
* Shared/WebPageCreationParameters.h:

If the WebProcess has crashed since the last load, change reload and the various back/forward APIs to 
update the current back/forward item (if necessary) then relaunch the process:
* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::reattachToWebProcessWithItem):
(WebKit::WebPageProxy::reattachToWebProcess): Renamed from "relaunch()" and made private.
(WebKit::WebPageProxy::initializeWebPage):
(WebKit::WebPageProxy::loadURL):
(WebKit::WebPageProxy::loadURLRequest):
(WebKit::WebPageProxy::reload):
(WebKit::WebPageProxy::goForward):
(WebKit::WebPageProxy::goBack):
(WebKit::WebPageProxy::goToBackForwardItem):
(WebKit::WebPageProxy::creationParameters):
* UIProcess/WebPageProxy.h:

Rename "RestoreSession" to "RestoreSessionAndNavigateToCurrentItem"
* WebProcess/WebPage/WebPage.messages.in:
* UIProcess/cf/WebPageProxyCF.cpp:
(WebKit::WebPageProxy::restoreFromSessionStateData):

Restore a session on page creation if the parameters include it:
* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::WebPage): Call restoreSession if session state exists.
(WebKit::WebPage::restoreSessionAndNavigateToCurrentItem):
(WebKit::WebPage::restoreSession):
* WebProcess/WebPage/WebPage.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@75631 268f45cc-cd09-0410-ab3c-d52691b4dbfc