posix: directories should only be readable by the user.

base/file_util.h

Index: base/file_util.h
diff --git a/base/file_util.h b/base/file_util.h
index 47254ab2bd892945c472e29df39a3d238191fd85..3d072297482ce5a9a9d066ba9ffe0d02d3933f62 100644
--- a/base/file_util.h
+++ b/base/file_util.h
@@ -316,7 +316,7 @@ bool CreateNewTempDirectory(const std::wstring& prefix,
 
 // Creates a directory, as well as creating any parent directories, if they
 // don't exist. Returns 'true' on successful creation, or if the directory
-// already exists.
+// already exists.  The directory is only readable by the current user.
 bool CreateDirectory(const FilePath& full_path);
 // Deprecated temporary compatibility function.
 bool CreateDirectory(const std::wstring& full_path);