Reviewed by Sam Weinig.

        Send Update and DidUpdate messages
        https://bugs.webkit.org/show_bug.cgi?id=52316

        * UIProcess/DrawingAreaProxy.h:
        (WebKit::DrawingAreaProxy::update):
        Add empty stub.

        * UIProcess/DrawingAreaProxy.messages.in:
        Add Update message.

        * UIProcess/DrawingAreaProxyImpl.cpp:
        (WebKit::DrawingAreaProxyImpl::update):
        Just send back a DidUpdate message.

        * WebProcess/WebPage/DrawingArea.h:
        (WebKit::DrawingArea::didUpdate):
        Add empty stub.

        * WebProcess/WebPage/DrawingArea.messages.in:
        Add DidUpdate message.

        * WebProcess/WebPage/DrawingAreaImpl.cpp:
        (WebKit::DrawingAreaImpl::didUpdate):
        Call display().

        (WebKit::DrawingAreaImpl::display):
        Send an Update message.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@75630 268f45cc-cd09-0410-ab3c-d52691b4dbfc