Corrected attribute name in createBufferMapped deprecation warning

The "mapAtCreation" attribute that the warning currently recommends
doesn't exist. Spec and Blink implementation both specify that the
correct name is "mappedAtCreation".

Change-Id: Ibd4eafac535390afe410d55d5ce922c8d7ae2247
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2363267
Commit-Queue: Brandon Jones <bajones@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Auto-Submit: Brandon Jones <bajones@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799150}

third_party/blink/renderer/modules/webgpu/gpu_device.cc

@@ -163,7 +163,7 @@ HeapVector<GPUBufferOrArrayBuffer> GPUDevice::createBufferMapped(
     const GPUBufferDescriptor* descriptor,
     ExceptionState& exception_state) {
   AddConsoleWarning(
-      "createBufferMapped is deprecated: use mapAtCreation instead");
+      "createBufferMapped is deprecated: use mappedAtCreation instead");
 
   GPUBuffer* gpu_buffer;
   DOMArrayBuffer* array_buffer;