Clang style plugin: add warn-only option and use it on Windows

tools/clang/plugins/tests/warn_only.h

Index: tools/clang/plugins/tests/warn_only.h
diff --git a/tools/clang/plugins/tests/warn_only.h b/tools/clang/plugins/tests/warn_only.h
new file mode 100644
index 0000000000000000000000000000000000000000..fcc0aa1dba2b7a19a15098ae41a9a3c2067555da
--- /dev/null
+++ b/tools/clang/plugins/tests/warn_only.h
@@ -0,0 +1,21 @@
+// Copyright (c) 2015 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.
+
+#ifndef WARN_ONLY_H_
+#define WARN_ONLY_H_
+
+#include <string>
+#include <vector>
+
+class InlineCtors {
+ public:
+  InlineCtors() {}
+  ~InlineCtors() {}
+
+ private:
+  std::vector<int> one_;
+  std::vector<std::string> two_;
+};
+
+#endif  // WARN_ONLY_H_