[dawn][emscripten] Fixes assert for undefined default in surface.Configure.

No-Try: True
Change-Id: I6b9ec8db18c716284a92d433ace1f083293c2d52
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/235934
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Auto-Submit: Loko Kung <lokokung@google.com>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>

third_party/emdawnwebgpu/library_webgpu.js

diff --git a/third_party/emdawnwebgpu/library_webgpu.js b/third_party/emdawnwebgpu/library_webgpu.js
index 5a86163..5a6a564 100644
--- a/third_party/emdawnwebgpu/library_webgpu.js
+++ b/third_party/emdawnwebgpu/library_webgpu.js
@@ -2441,8 +2441,9 @@
     var context = WebGPU.getJsObject(surfacePtr);
 
 #if ASSERTIONS
-    assert({{{ gpu.PresentMode.Fifo }}} ===
-      {{{ gpu.makeGetU32('config', C_STRUCTS.WGPUSurfaceConfiguration.presentMode) }}});
+    var presentMode = {{{ gpu.makeGetU32('config', C_STRUCTS.WGPUSurfaceConfiguration.presentMode) }}};
+    assert(presentMode === {{{ gpu.PresentMode.Fifo }}} ||
+           presentMode === {{{ gpu.PresentMode.Undefined }}});
 #endif
 
     var canvasSize = [