Allow POSIX callers to specify a new file's mode.

base/files/file_util_posix.cc

Index: base/files/file_util_posix.cc
diff --git a/base/files/file_util_posix.cc b/base/files/file_util_posix.cc
index d86d9bcc7e94f2067b35ae74855d55a4d1bee290..1494c6a5f26d86a92ba76ffe8d988f4365459745 100644
--- a/base/files/file_util_posix.cc
+++ b/base/files/file_util_posix.cc
@@ -695,6 +695,15 @@ int WriteFile(const FilePath& filename, const char* data, int size) {
   return bytes_written;
 }
 
+bool WriteFileWithMode(const FilePath& filename, const char* data, int size,
+                       mode_t mode) {
+  ThreadRestrictions::AssertIOAllowed();
+  ScopedFD file(HANDLE_EINTR(creat(filename.value().c_str(), mode)));
+  if (!file.is_valid())
+    return false;
+  return WriteFileDescriptor(file.get(), data, size);
+}
+
 bool WriteFileDescriptor(const int fd, const char* data, int size) {
   // Allow for partial writes.
   ssize_t bytes_written_total = 0;