Add utils/WGPUHelpers.{cpp,h} to CMake build

These files were added in this recent commit:
https://dawn-review.googlesource.com/c/dawn/+/68282

Change-Id: I63a64cea1946b3fe48ac20d478f9b7664bc63de0
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/68560
Commit-Queue: James Price <jrprice@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
diff --git a/src/dawn_native/CMakeLists.txt b/src/dawn_native/CMakeLists.txt
index 2c2ead4..6302a28 100644
--- a/src/dawn_native/CMakeLists.txt
+++ b/src/dawn_native/CMakeLists.txt
@@ -176,6 +176,8 @@
     "VertexFormat.cpp"
     "VertexFormat.h"
     "dawn_platform.h"
+    "utils/WGPUHelpers.cpp"
+    "utils/WGPUHelpers.h"
 )
 target_link_libraries(dawn_native
     PUBLIC dawncpp_headers