message: Trigger GC Sweeps on Vulkan
  Vulkan backend wasn't making a call to Tick(), meaning that
  vkDestroy* operations were being enqueued, but never executed.
diff: @@ -28,6 +28,8 @@ namespace dawn_native { namespace vulkan {
  void Queue::SubmitImpl(uint32_t numCommands, CommandBufferBase* const* commands) {
  Device* device = ToBackend(GetDevice());
  + device->Tick();
  +
  VkCommandBuffer commandBuffer = device->GetPendingCommandBuffer();
  for (uint32_t i = 0; i < numCommands; ++i) {
  ToBackend(commands[i])->RecordCommands(commandBuffer);
  