Makes the script a bit more accurate in identifying place-holder header files. Bug: None Change-Id: Iba13562aed0d40bffef9c25d7345f3bb8af16c29 No-Try: true Reviewed-on: https://webrtc-review.googlesource.com/4381 Reviewed-by: Patrik Höglund <phoglund@webrtc.org> Commit-Queue: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20357}