[Mac] tag the video layers with descriptive name to aid debugging

[Mac] tag the video layers with descriptive name to aid debugging
https://bugs.webkit.org/show_bug.cgi?id=132371

Reviewed by Darin Adler.

Source/WebCore:
* platform/graphics/avfoundation/objc/MediaPlayerPrivateAVFoundationObjC.mm:
(WebCore::MediaPlayerPrivateAVFoundationObjC::createVideoLayer): Set the AVPlayerLayer
    name in a debug build.

Source/WebKit2:
* WebProcess/ios/WebVideoFullscreenManager.mm:
(WebKit::WebVideoFullscreenManager::enterFullscreenForNode): Set the
    fullscreen host layer name in a debug build.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167977 268f45cc-cd09-0410-ab3c-d52691b4dbfc