Attempt at synchronizing swap image writes between the main window and graphics backend.

Disabled for now due to device timeouts.

src/xenia/ui/vulkan/vulkan_swap_chain.h

@@ -53,6 +53,9 @@ class VulkanSwapChain {
   // torn down and recreated with the new surface properties (size/etc).
   bool Reinitialize();
 
+  // Waits on and signals a semaphore in this operation.
+  void WaitAndSignalSemaphore(VkSemaphore sem);
+
   // Begins the swap operation, preparing state for rendering.
   bool Begin();
   // Ends the swap operation, finalizing rendering and presenting the results.
@@ -86,6 +89,7 @@ class VulkanSwapChain {
   VkSemaphore image_usage_semaphore_ = nullptr;
   uint32_t current_buffer_index_ = 0;
   std::vector<Buffer> buffers_;
+  std::vector<VkSemaphore> wait_and_signal_semaphores_;
 };
 
 }  // namespace vulkan