Add the ability to change the working directory

runtime/bin/directory_macos.cc

Index: runtime/bin/directory_macos.cc
diff --git a/runtime/bin/directory_macos.cc b/runtime/bin/directory_macos.cc
index 5c7b115964930333f8634233db546ccaec7e6772..3a9ab0462e2524fc0e7e031a23c703a4a7a8a442 100644
--- a/runtime/bin/directory_macos.cc
+++ b/runtime/bin/directory_macos.cc
@@ -420,6 +420,12 @@ char* Directory::Current() {
 }
 
 
+bool Directory::SetCurrent(const char* path) {
+  int result = TEMP_FAILURE_RETRY(chdir(path));
+  return result == 0;
+}
+
+
 bool Directory::Create(const char* dir_name) {
   // Create the directory with the permissions specified by the
   // process umask.