Need WebKit2 API to asynchronously get the resource data for a URL

Reviewed by Maciej Stachowiak. 

Rename WKFrameGetMainResourceDataFunction to WKFrameGetResourceDataFunction, and add
new API to get a resource by URL:
* UIProcess/API/C/WKFrame.cpp:
(WKFrameGetMainResourceData):
(WKFrameGetResourceData):
(callGetResourceDataBlockAndDispose):
(WKFrameGetMainResourceData_b):
(WKFrameGetResourceData_b):
* UIProcess/API/C/WKFrame.h:

Implement the new API in the UIProcess side:
* UIProcess/WebFrameProxy.cpp:
(WebKit::WebFrameProxy::getResourceData):
* UIProcess/WebFrameProxy.h:
* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::getResourceDataFromFrame):
* UIProcess/WebPageProxy.h:

Have the WebProcess get the data and call back to the UIProcess:
* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::getResourceDataFromFrame):
* WebProcess/WebPage/WebPage.h:
* WebProcess/WebPage/WebPage.messages.in:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@76087 268f45cc-cd09-0410-ab3c-d52691b4dbfc