[dawn][emscripten] Default featureLevel should be undefined.

- Making the default featureLevel = undefined should fix
  Chrome builds < M133.

No-Try: true
Change-Id: I5d3975aef2723df7d807d82a610223e467c625a9
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/223017
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Loko Kung <lokokung@google.com>
Auto-Submit: Loko Kung <lokokung@google.com>
diff --git a/third_party/emdawnwebgpu/library_webgpu.js b/third_party/emdawnwebgpu/library_webgpu.js
index 842d313..5862ce4 100644
--- a/third_party/emdawnwebgpu/library_webgpu.js
+++ b/third_party/emdawnwebgpu/library_webgpu.js
@@ -1943,7 +1943,7 @@
       {{{ gpu.makeCheckDescriptor('options') }}}
       var featureLevel = {{{ gpu.makeGetU32('options', C_STRUCTS.WGPURequestAdapterOptions.featureLevel) }}};
       opts = {
-        "featureLevel": featureLevel === {{{ gpu.FeatureLevel.Compatibility }}} ? "compatibility" : "core",
+        "featureLevel": featureLevel === {{{ gpu.FeatureLevel.Compatibility }}} ? "compatibility" : undefined,
         "powerPreference": WebGPU.PowerPreference[
           {{{ gpu.makeGetU32('options', C_STRUCTS.WGPURequestAdapterOptions.powerPreference) }}}],
         "forceFallbackAdapter":