Windows: Fix --enable-logging to not disable logging when stderr is a pipe

base/process_util_win.cc

Index: base/process_util_win.cc
diff --git a/base/process_util_win.cc b/base/process_util_win.cc
index 3ac2ca4de7ba88ef635a755303d56f10392f1344..6cbc887fb5277d9d773fdc6426474d70fa0b49a5 100644
--- a/base/process_util_win.cc
+++ b/base/process_util_win.cc
@@ -122,6 +122,24 @@ void TimerExpiredTask::KillProcess() {
 }  // namespace
 
 void RouteStdioToConsole() {
+  // Don't change anything if stdout or stderr already point to a
+  // valid stream.
+  //
+  // If we are running under Buildbot or under Cygwin's default
+  // terminal (mintty), stderr and stderr will be pipe handles.  In
+  // that case, we don't want to open CONOUT$, because its output
+  // likely does not go anywhere.
+  //
+  // We don't use GetStdHandle() to check stdout/stderr here because
+  // it can return dangling IDs of handles that were never inherited
+  // by this process.  These IDs could have been reused by the time
+  // this function is called.  The CRT checks the validity of
+  // stdout/stderr on startup (before the handle IDs can be reused).
+  // _fileno(stdout) will return -2 (_NO_CONSOLE_FILENO) if stdout was
+  // invalid.
+  if (_fileno(stdout) >= 0 || _fileno(stderr) >= 0)
+    return;
+
   if (!AttachConsole(ATTACH_PARENT_PROCESS)) {
     unsigned int result = GetLastError();
     // Was probably already attached.