Stop overwriting errno in base::StringPrintf, StringAppendV, and StringToDouble

base/scoped_clear_errno_unittest.cc

Index: base/scoped_clear_errno_unittest.cc
diff --git a/base/scoped_clear_errno_unittest.cc b/base/scoped_clear_errno_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ff69bddbbdaeb635a742d9682d54aaaf7a77292c
--- /dev/null
+++ b/base/scoped_clear_errno_unittest.cc
@@ -0,0 +1,26 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <errno.h>
+
+#include "base/scoped_clear_errno.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+TEST(ScopedClearErrno, TestNoError) {
+  errno = 1;
+  {
+    ScopedClearErrno clear_error;
+    EXPECT_EQ(0, errno);
+  }
+  EXPECT_EQ(1, errno);
+}
+
+TEST(ScopedClearErrno, TestError) {
+  errno = 1;
+  {
+    ScopedClearErrno clear_error;
+    errno = 2;
+  }
+  EXPECT_EQ(2, errno);
+}