Add missing include guard to test_overscroll_delegate.h

Change-Id: I3a9785519bfe9d6b10972bbe7b70a3c9c3f5fdbc
Reviewed-on: https://chromium-review.googlesource.com/842803Reviewed-by: Camille Lamy <clamy@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#526029}

content/test/test_overscroll_delegate.h

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef CONTENT_TEST_TEST_OVERSCROLL_DELEGATE_H_
+#define CONTENT_TEST_TEST_OVERSCROLL_DELEGATE_H_
+
 #include <vector>
 
 #include "base/optional.h"
@@ -52,3 +55,5 @@ class TestOverscrollDelegate : public OverscrollControllerDelegate {
 };
 
 }  // namespace content
+
+#endif  // CONTENT_TEST_TEST_OVERSCROLL_DELEGATE_H_