message: D3D12 Immediately release pending commands
  We want to release pending commands in Device::WaitForIdleForDestruction()
  so that when we call TickImpl(), we can reset the command allocators.
diff: @@ -416,6 +416,9 @@ namespace dawn_native { namespace d3d12 {
  }
  MaybeError Device::WaitForIdleForDestruction() {
  + // Immediately forget about all pending commands
  + mPendingCommands.Release();
  +
  DAWN_TRY(NextSerial());
  // Wait for all in-flight commands to finish executing
  DAWN_TRY(WaitForSerial(mLastSubmittedSerial));
  