[tint] Migrate GN build over to generated files/deps

Change-Id: Ia38585b941c847db6c8e31c78c1f648d07f6f0c8
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/143340
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
diff --git a/tint_overrides_with_defaults.gni b/tint_overrides_with_defaults.gni
index 977e433..dca626e 100644
--- a/tint_overrides_with_defaults.gni
+++ b/tint_overrides_with_defaults.gni
@@ -27,6 +27,11 @@
     tint_spirv_tools_dir = "//third_party/vulkan-deps/spirv-tools/src"
   }
 
+  # Path to glslang checkout
+  if (!defined(tint_glslang_dir)) {
+    tint_glslang_dir = "//third_party/vulkan-deps/glslang/src"
+  }
+
   # Path to googletest checkout
   if (!defined(tint_googletest_dir)) {
     tint_googletest_dir = "//third_party/googletest"
@@ -87,3 +92,10 @@
     tint_build_unittests = true
   }
 }
+
+declare_args() {
+  # Directory holding tint source
+  if (!defined(tint_src_dir)) {
+    tint_src_dir = "${tint_root_dir}/src/tint"
+  }
+}