Summary: public There is really no reason NativeViewHierarchyManager.addRootView() should be performed synchroniously when called from background thread, as long as it is executed before every other command in UIViewOperationQueue, and we can ensure that by putting add view command at the front of the queue. When that happpens, the queue should always be empty anyway, but it's best to be safe.
This eliminates an unnecessary blocking call and should overall make the code simpler and safer (Semaphores can timeout).
Reviewed By: astreet
Differential Revision: D2462680
fb-gh-sync-id: 784ac6573a455019b93628c70992f3830b9d6f1f
aeda31428d