[Impeller] Remove unactionable error logs and use structure chains fo…

…r instance creation.

I didn't know this when I wrote it initially but structure chains will
throw a compile time error if a chain member violates the Vulkan spec.
pNext chaining is easy to mess up otherwise and we should use structure
chains where possible. We are already doing this during pipeline
construction.

impeller/renderer/backend/vulkan/context_vk.cc

@@ -185,28 +185,21 @@ void ContextVK::Setup(Settings settings) {
   application_info.setPEngineName("Impeller");
   application_info.setPApplicationName("Impeller");
 
+  vk::StructureChain<vk::InstanceCreateInfo, vk::ValidationFeaturesEXT>
+      instance_chain;
+
+  if (!caps->AreValidationsEnabled()) {
+    instance_chain.unlink<vk::ValidationFeaturesEXT>();
+  }
+
   std::vector<vk::ValidationFeatureEnableEXT> enabled_validations = {
       vk::ValidationFeatureEnableEXT::eSynchronizationValidation,
   };
 
-  vk::ValidationFeaturesEXT validation;
+  auto validation = instance_chain.get<vk::ValidationFeaturesEXT>();
   validation.setEnabledValidationFeatures(enabled_validations);
 
-  vk::InstanceCreateInfo instance_info;
-  if (caps->AreValidationsEnabled()) {
-    std::stringstream ss;
-    ss << "Enabling validation layers, features: [";
-    for (const auto& validation : enabled_validations) {
-      ss << vk::to_string(validation) << " ";
-    }
-    ss << "]";
-    FML_LOG(ERROR) << ss.str();
-#if !defined(IMPELLER_ENABLE_VULKAN_VALIDATION_LAYERS) && FML_OS_ANDROID
-    FML_LOG(ERROR) << "Vulkan validation layers turned on but the gn argument "
-                      "`--enable-vulkan-validation-layers` is missing.";
-#endif
-    instance_info.pNext = &validation;
-  }
+  auto instance_info = instance_chain.get<vk::InstanceCreateInfo>();
   instance_info.setPEnabledLayerNames(enabled_layers_c);
   instance_info.setPEnabledExtensionNames(enabled_extensions_c);
   instance_info.setPApplicationInfo(&application_info);