make ScopedAllowWait available from DispatcherHost
make ScopedAllowWait available from DispatcherHost

ondra-novak/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,littlstar/chromium.src