Fix copyright headers in GN files

Fixes a few more copyright headers that were missed earlier because
PanProjectChecks() doesn't consider GN files as source files.

Bug: pdfium:1884
Change-Id: I0d0f47750d1760bfea1f9aa8831f87accf2725c3
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/100630
Auto-Submit: K. Moon <kmoon@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: K. Moon <kmoon@chromium.org>
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index bc0a914..15c11c7 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -498,6 +498,19 @@
       input_api.canned_checks.PanProjectChecks(
           input_api, output_api, project_name='PDFium'))
 
+  # PanProjectChecks() doesn't consider .gn/.gni files, so check those, too.
+  files_to_check = (
+      r'.*\.gn$',
+      r'.*\.gni$',
+  )
+  results.extend(
+      input_api.canned_checks.CheckLicense(
+          input_api,
+          output_api,
+          project_name='PDFium',
+          source_file_filter=lambda x: input_api.FilterSourceFile(
+              x, files_to_check=files_to_check)))
+
   return results