Add missing header to gni file.

Change-Id: I7def5f224be502d20e36d8cc11b4c60584485e31
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/547824
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Jorge Betancourt <jmbetancourt@google.com>
Commit-Queue: Jorge Betancourt <jmbetancourt@google.com>
1 file changed