Add the methods to change and get a posix file permission to file_util.

base/file_util_posix.cc

Index: base/file_util_posix.cc
diff --git a/base/file_util_posix.cc b/base/file_util_posix.cc
index e3bab95dd8e32554c81d8b41466909e5406e0027..8647df5edca9049b37f3b4a429dcc2f39f405260 100644
--- a/base/file_util_posix.cc
+++ b/base/file_util_posix.cc
@@ -457,6 +457,60 @@ bool ReadSymbolicLink(const FilePath& symlink_path,
   return true;
 }
 
+bool GetPosixFilePermissions(const FilePath& path, int* mode) {
+  base::ThreadRestrictions::AssertIOAllowed();
+  DCHECK(mode);
+
+  stat_wrapper_t file_info;
+  // Uses stat(), because on symbolic link, lstat() may not return valid
+  // information in the permission bits st_mode.
+  if (CallStat(path.value().c_str(), &file_info) != 0)
+    return false;
+
+  *mode = file_info.st_mode & FILE_PERMISSION_MASK;
+  return true;
+}
+
+bool SetPosixFilePermissions(const FilePath& path,
+                             int mode) {
+  base::ThreadRestrictions::AssertIOAllowed();
+  DCHECK((mode & ~FILE_PERMISSION_MASK) == 0);
+
+  stat_wrapper_t stat_buf;
+  if (CallStat(path.value().c_str(), &stat_buf) != 0)
+    return false;
+
+  mode_t updated_mode_bits = stat_buf.st_mode & ~FILE_PERMISSION_MASK;
+  updated_mode_bits |= mode & FILE_PERMISSION_MASK;
+
+  if (HANDLE_EINTR(chmod(path.value().c_str(), updated_mode_bits)) != 0)
+    return false;
+
+  return true;
+}
+
+bool ChangePosixFilePermissions(const FilePath& path,
+                                int mode_bits_to_set,
+                                int mode_bits_to_clear) {
+  base::ThreadRestrictions::AssertIOAllowed();
+  DCHECK((mode_bits_to_set & ~FILE_PERMISSION_MASK) == 0);
+  DCHECK((mode_bits_to_clear & ~FILE_PERMISSION_MASK) == 0);
+  DCHECK(!(mode_bits_to_set & mode_bits_to_clear))
+      << "Can't set and clear the same bits.";
+
+  int mode;
+  if (!GetPosixFilePermissions(path, &mode))
+    return false;
+
+  mode |= mode_bits_to_set;
+  mode &= ~mode_bits_to_clear;
+
+  if (SetPosixFilePermissions(path, mode))
+    return false;
+
+  return true;
+}
+
 // Creates and opens a temporary file in |directory|, returning the
 // file descriptor. |path| is set to the temporary file path.
 // This function does NOT unlink() the file.