message: Fix MSVC build error due to implicit descriptor heap offset cast.
diff: @@ -72,7 +72,8 @@ namespace dawn_native { namespace d3d12 {
  ? RingBufferAllocator::kInvalidOffset
  : heapInfo->allocator.Allocate(count, pendingSerial);
  if (startOffset != RingBufferAllocator::kInvalidOffset) {
  - return DescriptorHeapHandle{heapInfo->heap, mSizeIncrements[type], startOffset};
  + return DescriptorHeapHandle{heapInfo->heap, mSizeIncrements[type],
  + static_cast<uint32_t>(startOffset)};
  }
  // If the pool has no more space, replace the pool with a new one of the specified size
  