Add deprecation warning for setSubData

Bug: 1069302
Change-Id: Icdb36c751374aeb968071fb0a57993f000745182
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2147872Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758584}

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

@@ -131,6 +131,10 @@ void GPUBuffer::setSubData(uint64_t dst_byte_offset,
                            uint64_t src_byte_offset,
                            uint64_t byte_length,
                            ExceptionState& exception_state) {
+  device_->AddConsoleWarning(
+      "GPUBuffer.setSubData is deprecated: use createBufferMapped "
+      "(with copyBufferToBuffer if needed) "
+      "(but note the design/spec of this API is still in flux)");
   const uint8_t* src_base =
       reinterpret_cast<const uint8_t*>(src.BaseAddressMaybeOnStack());
   size_t src_byte_length = src.ByteLengthAsSizeT();