[chromium] Add isOrphan() to the WebLayer API
https://bugs.webkit.org/show_bug.cgi?id=112649

Reviewed by James Robinson.

This method will be used by WebMediaPlayerClientImpl to tell
if the compositing video layer is currently being used to
display the video content or not.

* chromium/public/WebLayer.h:
(WebLayer):


git-svn-id: https://svn.webkit.org/repository/webkit/trunk/Source/Platform/chromium/public@146487 268f45cc-cd09-0410-ab3c-d52691b4dbfc