This will allow to ensure that fidl and mojom files have proper
copyright header.

Bug: 831384
Change-Id: I5e41bbf27f2e3f2c6749a52de7463d651d033b81
Reviewed-on: https://chromium-review.googlesource.com/1036606Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>