FSceneRenderTargets::AllocateCommonDepthTargets gives the HMD the option to create the depth/stencil textures. When following that path (e.g. with the OculusHMD plugin), FRenderTargetPool::FindFreeElement will (the first time through) create the resource, which will be immediately discarded if the HMD created one. The fix was to add a boolean flag to FRenderTargetPool::FindFreeElement to signal deferred resource creation to avoid this extra create/destroy cycle.
#jira UE-74476
#rb ryan.vance
[CL 6415079 by steve smith in Dev-VR branch]
