Fix GN args merge issue for https://codereview.chromium.org/265693003

tools/gn/command_args.cc

Index: tools/gn/command_args.cc
diff --git a/tools/gn/command_args.cc b/tools/gn/command_args.cc
index 9501681fe2de91071c76c64334e9d78c3d87f03f..65edc20a9d2abecaa6001c0636d4b1fbb3d93e9a 100644
--- a/tools/gn/command_args.cc
+++ b/tools/gn/command_args.cc
@@ -198,7 +198,7 @@ bool RunEditor(const base::FilePath& file_to_edit) {
 
 #else  // POSIX
 
-void RunEditor(const base::FilePath& file_to_edit) {
+bool RunEditor(const base::FilePath& file_to_edit) {
   // Prefer $VISUAL, then $EDITOR, then vi.
   const char* editor_ptr = getenv("VISUAL");
   if (!editor_ptr)