message: Typo fix: `==` should be `=`.
  Discovered accidentally while building on Windows, via a compiler warning.
diff: @@ -378,7 +378,7 @@ int SubProcess::Communicate(const string* stdin_input, string* stdout_output,
  }
  } else {
  CloseHandle(parent_pipe_[CHAN_STDIN]);
  - parent_pipe_[CHAN_STDIN] == NULL;
  + parent_pipe_[CHAN_STDIN] = NULL;
  }
  if (parent_pipe_[CHAN_STDOUT] != nullptr) {
  