Add WKPageLoadData and WKPageLoadDataWithUserData SPI to support loading arbitrary...

Add WKPageLoadData and WKPageLoadDataWithUserData SPI to support loading arbitrary data blobs
https://bugs.webkit.org/show_bug.cgi?id=116325

Reviewed by Simon Fraser.

* UIProcess/API/C/WKPage.cpp:
(WKPageLoadData):
(WKPageLoadDataWithUserData):
Add new SPI.

* UIProcess/API/C/WKPage.h:
* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::loadData):
* UIProcess/WebPageProxy.h:
Pipe through to the WebProcess.

* WebProcess/WebPage/WebPage.h:
* WebProcess/WebPage/WebPage.messages.in:
* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::loadDataImpl):
(WebKit::WebPage::loadData):
(WebKit::WebPage::loadHTMLString):
(WebKit::WebPage::loadAlternateHTMLString):
(WebKit::WebPage::loadPlainTextString):
(WebKit::WebPage::loadWebArchiveData):
Rename existing loadData function to loadDataImpl (I hate it) to avoid overload conflict
from IPC magic.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@150271 268f45cc-cd09-0410-ab3c-d52691b4dbfc