Vendor dependencies for 0.3.0 release

vendor/wgpu-core/src/hal_api.rs

@@ -0,0 +1,29 @@
+use wgt::{Backend, WasmNotSendSync};
+
+pub trait HalApi: hal::Api + 'static + WasmNotSendSync {
+    const VARIANT: Backend;
+}
+
+impl HalApi for hal::api::Empty {
+    const VARIANT: Backend = Backend::Empty;
+}
+
+#[cfg(vulkan)]
+impl HalApi for hal::api::Vulkan {
+    const VARIANT: Backend = Backend::Vulkan;
+}
+
+#[cfg(metal)]
+impl HalApi for hal::api::Metal {
+    const VARIANT: Backend = Backend::Metal;
+}
+
+#[cfg(dx12)]
+impl HalApi for hal::api::Dx12 {
+    const VARIANT: Backend = Backend::Dx12;
+}
+
+#[cfg(gles)]
+impl HalApi for hal::api::Gles {
+    const VARIANT: Backend = Backend::Gl;
+}