Normalize DEPS to ease merging with Dawn

- Format specific targets to have the hash in the target rule instead
  of a variable.
- Only have the base part of the URL in a variable
- Use vulkan-deps instead of individual DEPS (spirv-tools,
  spirv-headers & glslang)

BUG=tint:1481

Change-Id: I871a656e26050698da2c77f4f39fec94a9c4f8a4
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/84723
Reviewed-by: David Neto <dneto@google.com>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
diff --git a/tint_overrides_with_defaults.gni b/tint_overrides_with_defaults.gni
index e952005..9680e35 100644
--- a/tint_overrides_with_defaults.gni
+++ b/tint_overrides_with_defaults.gni
@@ -24,7 +24,7 @@
 
   # Path to spirv-tools checkout
   if (!defined(tint_spirv_tools_dir)) {
-    tint_spirv_tools_dir = "//third_party/spirv-tools"
+    tint_spirv_tools_dir = "//third_party/vulkan-deps/spirv-tools/src"
   }
 
   # Path to googletest checkout
@@ -34,7 +34,7 @@
 
   # Path to spirv-headers checkout
   if (!defined(tint_spirv_headers_dir)) {
-    tint_spirv_headers_dir = "//third_party/spirv-headers"
+    tint_spirv_headers_dir = "//third_party/vulkan-deps/spirv-headers/src"
   }
 
   # Build the SPIR-V input reader