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 561f5c7e6615ac45fcd7e44ea35ab9a4343bc4a8..58d86772616aeaf2ab5b6d5a13eaaf969b8ff2bf 100644
--- a/base/files/file_util_posix.cc
+++ b/base/files/file_util_posix.cc
@@ -677,8 +677,13 @@ int ReadFile(const FilePath& filename, char* data, int max_size) {
 }
 
 int WriteFile(const FilePath& filename, const char* data, int size) {
+  return WriteFileMode(filename, data, size, 0640);
+}
+
+int WriteFileMode(const FilePath& filename, const char* data, int size,
+                  mode_t mode) {
   ThreadRestrictions::AssertIOAllowed();
-  int fd = HANDLE_EINTR(creat(filename.value().c_str(), 0640));
+  int fd = HANDLE_EINTR(creat(filename.value().c_str(), mode));
   if (fd < 0)
     return -1;