Change base directory for CTS runner, part 1

Changes the test page to expect files to be served from BUILD_DIR
to BUILD_DIR/gen/third_party/dawn. Serving only the subdirectory
shaves multiple seconds off of harness startup in local builds.

Bug: chromium:1338672
Change-Id: I29927e8d0928874fe780f9b15910b0d2eed97833
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/94580
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Brian Sheedy <bsheedy@google.com>
diff --git a/webgpu-cts/test_page.html b/webgpu-cts/test_page.html
index 89ef8086..6b68101 100644
--- a/webgpu-cts/test_page.html
+++ b/webgpu-cts/test_page.html
@@ -17,6 +17,11 @@
 <meta charset=utf-8>
 <link rel=help href='https://gpuweb.github.io/gpuweb/'>
 
+<!-- Temporarily try to |setBaseResourcePath| from two paths as we migrate the base static server dir -->
+<script type=module>
+    import { setBaseResourcePath } from '/third_party/webgpu-cts/src/common/framework/resources.js';
+    setBaseResourcePath('/third_party/webgpu-cts/resources');
+</script>
 <script type=module>
     import { setBaseResourcePath } from '/gen/third_party/dawn/third_party/webgpu-cts/src/common/framework/resources.js';
     setBaseResourcePath('/gen/third_party/dawn/third_party/webgpu-cts/resources');