Fix the win_console_app build config.

This currently fail with the following error message:

../../chrome/app/chrome_exe_main_win.cc(190,31): error: use of undeclared identifier 'main'
  fiber_state->fiber_result = main();

Change-Id: I19cd98a6a4d8d8ece8f2dc9556cd91da13c7117b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461549Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Auto-Submit: Sébastien Marchand <sebmarchand@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#815276}

chrome/app/chrome_exe_main_win.cc

@@ -47,6 +47,11 @@
 #include "content/public/common/result_codes.h"
 #include "third_party/crashpad/crashpad/util/win/initial_client_data.h"
 
+#if defined(WIN_CONSOLE_APP)
+// Forward declaration of main.
+int main();
+#endif
+
 namespace {
 
 bool IsFastStartSwitch(const std::string& command_line_switch) {