No need to log to files from a console process

src/base/init_mozc.cc

@@ -31,6 +31,7 @@
 
 #ifdef _WIN32
 #include <windows.h>
+#include <winnt.h>
 #endif  // _WIN32
 
 #include <string>
@@ -59,6 +60,24 @@ ABSL_FLAG(std::string, log_dir, "",
 ABSL_FLAG(std::string, program_invocation_name, "",
           "Program name copied from argv[0].");
 
+#if defined(_WIN32)
+EXTERN_C IMAGE_DOS_HEADER __ImageBase;
+
+namespace {
+bool IsCuiProcess() {
+  const std::uintptr_t base_addr =
+      reinterpret_cast<std::uintptr_t>(&__ImageBase);
+  const auto *nt_header = reinterpret_cast<const IMAGE_NT_HEADERS *>(
+      base_addr + __ImageBase.e_lfanew);
+  if (nt_header->Signature != IMAGE_NT_SIGNATURE) {
+    return false;
+  }
+  return nt_header->OptionalHeader.Subsystem == IMAGE_SUBSYSTEM_WINDOWS_CUI;
+}
+}  // namespace
+#endif
+
+
 namespace mozc {
 namespace {
 
@@ -103,6 +122,10 @@ void ParseCommandLineFlags(int argc, char **argv) {
 void InitMozc(const char *arg0, int *argc, char ***argv) {
   absl::SetFlag(&FLAGS_program_invocation_name, *argv[0]);
 #ifdef _WIN32
+  if (IsCuiProcess()) {
+    absl::SetFlag(&FLAGS_logtostderr, true);
+  }
+
   // InitMozc() is supposed to be used for code generator or
   // other programs which are not included in the production code.
   // In these code, we don't want to show any error messages when