Clean background frame references every 20 submits

* This means the background references array won't build up even for programs
  that don't present.

renderdoc/driver/vulkan/vk_core.h

@@ -750,6 +750,8 @@ private:
   rdcarray<VkResourceRecord *> m_ForcedReferences;
   Threading::CriticalSection m_ForcedReferencesLock;
 
+  volatile int64_t m_QueueCounter = 0;
+
   rdcarray<VkResourceRecord *> GetForcedReferences()
   {
     rdcarray<VkResourceRecord *> ret;

renderdoc/driver/vulkan/wrappers/vk_queue_funcs.cpp

@@ -975,6 +975,12 @@ VkResult WrappedVulkan::vkQueueSubmit(VkQueue queue, uint32_t submitCount,
             sub->bakedCommands->AddResourceReferences(GetResourceManager());
         }
       }
+
+      // every 20 submits clean background references, in case the application isn't presenting.
+      if((Atomic::Inc64(&m_QueueCounter) % 20) == 0)
+      {
+        GetResourceManager()->CleanBackgroundFrameReferences();
+      }
     }
 
     if(capframe)