Reviewed by Sam Weinig.

        Suspend/resume painting as the WKView visibility changes
        https://bugs.webkit.org/show_bug.cgi?id=52738

        * UIProcess/DrawingAreaProxy.h:
        (WebKit::DrawingAreaProxy::visibilityDidChange):
        Add new member function. It should really be pure virtual once setPageIsVisible
        is removed.

        * UIProcess/DrawingAreaProxyImpl.cpp:
        (WebKit::DrawingAreaProxyImpl::visibilityDidChange):
        Send SuspendPainting/ResumePainting messages based on whether the view is visible or not.

        (WebKit::DrawingAreaProxyImpl::setPageIsVisible):
        Make this a stub; it should really be removed.

        * UIProcess/WebPageProxy.cpp:
        (WebKit::WebPageProxy::viewStateDidChange):
        Call visibilityDidChange.

        * UIProcess/WebPageProxy.h:
        (WebKit::WebPageProxy::isViewVisible):
        Add new getter.

        * WebProcess/WebPage/DrawingArea.messages.in:
        Add SuspendPainting and ResumePainting messages.

        * WebProcess/WebPage/DrawingAreaImpl.cpp:
        (WebKit::DrawingAreaImpl::DrawingAreaImpl):
        Initialize m_isPaintingSuspended.

        (WebKit::DrawingAreaImpl::suspendPainting):
        Set m_isPaintingSuspended to true and stop the display timer.

        (WebKit::DrawingAreaImpl::resumePainting):
        Set m_isPaintingSuspended to false.

        (WebKit::DrawingAreaImpl::scheduleDisplay):
        (WebKit::DrawingAreaImpl::display):
        Bail if m_isPaintingSuspended is true.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@76157 268f45cc-cd09-0410-ab3c-d52691b4dbfc