vulkan: make Get*LayerRef take a Layer

The only user-visible change should be improved error messages.

Bug: 27911856
Change-Id: Ie50a9d37f07b590026176642f2c67270225f9280
diff --git a/vulkan/libvulkan/layers_extensions.h b/vulkan/libvulkan/layers_extensions.h
index 899d600..32e1a67 100644
--- a/vulkan/libvulkan/layers_extensions.h
+++ b/vulkan/libvulkan/layers_extensions.h
@@ -61,8 +61,8 @@
 const VkExtensionProperties* GetLayerDeviceExtensions(const Layer& layer,
                                                       uint32_t& count);
 
-LayerRef GetInstanceLayerRef(const char* name);
-LayerRef GetDeviceLayerRef(const char* name);
+LayerRef GetInstanceLayerRef(const Layer& layer);
+LayerRef GetDeviceLayerRef(const Layer& layer);
 
 }  // namespace api
 }  // namespace vulkan