Adding Vulkan headers to third_party.

.gitmodules

diff --git a/.gitmodules b/.gitmodules
index 5c7fdcb..17f084a 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -22,3 +22,7 @@
 	path = third_party/flatbuffers
 	url = https://github.com/google/flatbuffers.git
 	shallow = true
+[submodule "third_party/vulkan-headers"]
+	path = third_party/vulkan-headers
+	url = https://github.com/KhronosGroup/Vulkan-Headers.git
+	shallow = true

third_party/vulkan-headers

diff --git a/third_party/vulkan-headers b/third_party/vulkan-headers
new file mode 160000
index 0000000..ba091ba
--- /dev/null
+++ b/third_party/vulkan-headers
@@ -0,0 +1 @@
+Subproject commit ba091ba6a947f79623b28fe8bfccdce1ab9fa467