Error reporting on File in dart:io

runtime/bin/file_macos.cc

Index: runtime/bin/file_macos.cc
diff --git a/runtime/bin/file_macos.cc b/runtime/bin/file_macos.cc
index 9b7093daff51e3fe6336ad217173c90e1ee9c5e3..6ce73b1a732be225a45434d7880b1b4da29a523e 100644
--- a/runtime/bin/file_macos.cc
+++ b/runtime/bin/file_macos.cc
@@ -105,7 +105,7 @@ off_t File::Length() {
 }
 
 
-File* File::Open(const char* name, FileOpenMode mode) {
+File* File::Open(const char* name, FileOpenMode mode, OSError* os_error) {
   int flags = O_RDONLY;
   if ((mode & kWrite) != 0) {
     flags = (O_RDWR | O_CREAT);
@@ -115,6 +115,10 @@ File* File::Open(const char* name, FileOpenMode mode) {
   }
   int fd = TEMP_FAILURE_RETRY(open(name, flags, 0666));
   if (fd < 0) {
+    if (os_error != NULL) {
+      os_error->errno_ = errno;
+      os_error->strerror_ = strerror(errno);
+    }
     return NULL;
   }
   if (((mode & kWrite) != 0) && ((mode & kTruncate) == 0)) {