gn2bp: add .S files to allowed sources

libunwind and boringssl libcrypto (which might be replaced by Android's
version later on) contain assembly files.

Test: //components/cronet/android:cronet
Change-Id: Ic794afebe2da4d2b79a17423c2c9fe29ce4ef0fb
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index 66a7fc7..8a15ee1 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -503,7 +503,7 @@
 
 def is_supported_source_file(name):
   """Returns True if |name| can appear in a 'srcs' list."""
-  return os.path.splitext(name)[1] in ['.c', '.cc', '.cpp', '.java', '.proto']
+  return os.path.splitext(name)[1] in ['.c', '.cc', '.cpp', '.java', '.proto', '.S']
 
 
 def create_proto_modules(blueprint, gn, target):