<rdar://problem/8557864>
https://bugs.webkit.org/show_bug.cgi?id=47938

Reviewed by Anders Carlsson.

* UIProcess/API/C/WKFrame.cpp:
(WKFrameCopyUnreachableURL):
* UIProcess/API/C/WKFrame.h:
Add accessor for the unreachableURL if one is set. It will only be
set during a loadAlternateHTMLString and will be unset on the next normal
didStartProvisionalLoadForFrame call.

* UIProcess/API/C/WKPage.cpp:
(WKPageLoadHTMLString): Remove whitespace.
(WKPageLoadAlternateHTMLString):
* UIProcess/API/C/WKPage.h:
Add function to load a string as "alternate", meant for use as error pages.

* UIProcess/WebFrameProxy.h:
(WebKit::WebFrameProxy::setUnreachableURL): 
(WebKit::WebFrameProxy::unreachableURL):
Add setter/getter for the unreachableURL.

* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::loadAlternateHTMLString):
Plumb through the call to loadAlternateHTMLString to the WebProcess
and set the main frame's unreachableURL. This does nothing if no pages
have ever been loaded in this page.

(WebKit::WebPageProxy::didStartProvisionalLoadForFrame):
If this is not a provisional load of substitute data for an unreachableURL
(e.g. someone who called WKPageLoadAlternateHTMLString), reset the
frame's unreachableURL.

* UIProcess/WebPageProxy.h:
* UIProcess/WebPageProxy.messages.in:
Update function signatures.

* WebProcess/WebCoreSupport/WebFrameLoaderClient.cpp:
(WebKit::WebFrameLoaderClient::dispatchDidStartProvisionalLoad):
Pass whether or not this is a load of SubstituteData for an unreachableURL
to the UIProcess.

* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::loadData):
(WebKit::WebPage::loadAlternateHTMLString):
* WebProcess/WebPage/WebPage.h:
* WebProcess/WebPage/WebPage.messages.in:
Plumb through the loading of the alternate HTML string. 



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@70097 268f45cc-cd09-0410-ab3c-d52691b4dbfc