Wait for all device work to finish before destroy VkDevice

src/gpu/vk/GrVkBackendContext.cpp

Index: src/gpu/vk/GrVkBackendContext.cpp
diff --git a/src/gpu/vk/GrVkBackendContext.cpp b/src/gpu/vk/GrVkBackendContext.cpp
index 9506da554648bbbe064a60ad81b032840f42a20a..f5cd08ca8b4f115be18f116baab07663d1c620c5 100644
--- a/src/gpu/vk/GrVkBackendContext.cpp
+++ b/src/gpu/vk/GrVkBackendContext.cpp
@@ -238,6 +238,7 @@ const GrVkBackendContext* GrVkBackendContext::Create() {
 }
 
 GrVkBackendContext::~GrVkBackendContext() {
+    vkDeviceWaitIdle(fDevice);
     vkDestroyDevice(fDevice, nullptr);
     fDevice = VK_NULL_HANDLE;
     vkDestroyInstance(fInstance, nullptr);