Trigger GC Sweeps on Vulkan

Vulkan backend wasn't making a call to Tick(), meaning that
vkDestroy* operations were being enqueued, but never executed.

Change-Id: I597f59d6a17ea4247a1a042a2b5a7997d2e95612
Bug: dawn:94
Reviewed-on: https://dawn-review.googlesource.com/c/4020
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Brandon Jones <brandon1.jones@intel.com>

src/dawn_native/vulkan/QueueVk.cpp

@@ -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);