.gn files in the API directories are part of the API too...

...since we can break users by changing the build targets they're
using.

BUG=webrtc:8445

Change-Id: Iaa549ce9802bd99639d8b966807ae2db43e7f14b
Reviewed-on: https://webrtc-review.googlesource.com/16460
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20471}
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index c72fc19..a6d41c6 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -157,18 +157,19 @@
 def CheckNativeApiHeaderChanges(input_api, output_api):
   """Checks to remind proper changing of native APIs."""
   files = []
-  for f in input_api.AffectedSourceFiles(input_api.FilterSourceFile):
-    if f.LocalPath().endswith('.h'):
-      for path in API_DIRS:
-        dn = os.path.dirname(f.LocalPath())
-        if path == 'api':
-          # Special case: Subdirectories included.
-          if dn == 'api' or dn.startswith('api/'):
-            files.append(f)
-        else:
-          # Normal case: Subdirectories not included.
-          if dn == path:
-            files.append(f)
+  source_file_filter = lambda x: input_api.FilterSourceFile(
+      x, white_list=[r'.+\.(gn|gni|h)$'])
+  for f in input_api.AffectedSourceFiles(source_file_filter):
+    for path in API_DIRS:
+      dn = os.path.dirname(f.LocalPath())
+      if path == 'api':
+        # Special case: Subdirectories included.
+        if dn == 'api' or dn.startswith('api/'):
+          files.append(f)
+      else:
+        # Normal case: Subdirectories not included.
+        if dn == path:
+          files.append(f)
 
   if files:
     return [output_api.PresubmitNotifyResult(API_CHANGE_MSG, files)]