Reviewed by John Sullivan.

        Would like a way to query WKPageRef for the current progress value
        https://bugs.webkit.org/show_bug.cgi?id=40310
        <rdar://problem/8071299>

        Add WKPageGetEstimatedProgress. Remove the progress parameter from the didChangeProgress
        loader client callback function.

        * UIProcess/API/C/WKPage.cpp:
        (WKPageGetEstimatedProgress):
        * UIProcess/API/C/WKPage.h:
        * UIProcess/WebLoaderClient.cpp:
        (WebKit::WebLoaderClient::didChangeProgress):
        * UIProcess/WebLoaderClient.h:
        * UIProcess/WebPageProxy.cpp:
        (WebKit::WebPageProxy::WebPageProxy):
        (WebKit::WebPageProxy::close):
        (WebKit::WebPageProxy::didStartProgress):
        (WebKit::WebPageProxy::didChangeProgress):
        (WebKit::WebPageProxy::didFinishProgress):
        (WebKit::WebPageProxy::processDidExit):
        * UIProcess/WebPageProxy.h:
        (WebKit::WebPageProxy::estimatedProgress):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@60853 268f45cc-cd09-0410-ab3c-d52691b4dbfc