Add the ability to change the working directory

runtime/bin/directory_linux.cc

Index: runtime/bin/directory_linux.cc
diff --git a/runtime/bin/directory_linux.cc b/runtime/bin/directory_linux.cc
index 67ac94714fc35df6b2b255f5e9ceb4c43f513711..f3c1ec2fe5806dd527e31800a441894110d759fd 100644
--- a/runtime/bin/directory_linux.cc
+++ b/runtime/bin/directory_linux.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.