Implement File.directory() and File.directorySync() to get

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 352b9d140abe01a309dac4833ec15ef92a3e38ac..a85d61d64890bcc2c31795df08e8fe9181e3a9e8 100644
--- a/runtime/bin/file_macos.cc
+++ b/runtime/bin/file_macos.cc
@@ -184,6 +184,16 @@ char* File::GetCanonicalPath(const char* pathname) {
 }
 
 
+char* File::GetContainingDirectory(char* pathname) {
+  ASSERT(Exists(pathname));
+  char* path = NULL;
+  do {
+    path = dirname(pathname);
+  } while (path == NULL && errno == EINTR);
+  return GetCanonicalPath(path);
+}
+
+
 const char* File::PathSeparator() {
   return "/";
 }