Add output reference to gen written files.

tools/gn/scheduler.cc

Index: tools/gn/scheduler.cc
diff --git a/tools/gn/scheduler.cc b/tools/gn/scheduler.cc
index 622019ef05635af0769107e0f7fa4e01ae31d451..db0929db09543c5736e29bfbf5759ef18154e81d 100644
--- a/tools/gn/scheduler.cc
+++ b/tools/gn/scheduler.cc
@@ -113,6 +113,11 @@ void Scheduler::AddWrittenFile(const SourceFile& file) {
   written_files_.push_back(file);
 }
 
+std::vector<SourceFile> Scheduler::GetWrittenFiles() const {
+  base::AutoLock lock(lock_);
+  return written_files_;
+}
+
 void Scheduler::AddUnknownGeneratedInput(const Target* target,
                                          const SourceFile& file) {
   base::AutoLock lock(lock_);