Fix protobuf's library .gitinore file.

Fix .gitignore file for protobuf library not to exclude file, that is checkid in into repo.

Bug=none.

Change-Id: I40c442252475dd818a9150793c2982a63f18767d
Reviewed-on: https://chromium-review.googlesource.com/1046965Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Patrik Höglund <phoglund@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556809}

third_party/protobuf/.gitignore

@@ -53,6 +53,7 @@ src/google/protobuf/util/**/*.pb.h
 *.pyc
 *.egg-info
 *_pb2.py
+!python/google/protobuf/descriptor_pb2.py
 python/*.egg
 python/.eggs/
 python/.tox

third_party/protobuf/patches/0021-Fix-protobuf-s-library-.gitinore-file.patch

+From db78edb2e3f0a60317b167b3a4002d0f5aa5a2a7 Mon Sep 17 00:00:00 2001
+From: Artem Titov <titovartem@chromium.org>
+Date: Mon, 7 May 2018 13:13:08 +0200
+Subject: [PATCH] Fix protobuf's library .gitinore file. Fix .gitignore file
+ for protobuf library not to exclude file, that is checkid in into repo.
+
+---
+ third_party/protobuf/.gitignore | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/third_party/protobuf/.gitignore b/third_party/protobuf/.gitignore
+index 51d092c72475..a130b8bcc028 100644
+--- a/third_party/protobuf/.gitignore
++++ b/third_party/protobuf/.gitignore
+@@ -53,6 +53,7 @@ src/google/protobuf/util/**/*.pb.h
+ *.pyc
+ *.egg-info
+ *_pb2.py
++!python/google/protobuf/descriptor_pb2.py
+ python/*.egg
+ python/.eggs/
+ python/.tox
+-- 
+2.17.0.441.gb46fe60e1d-goog
+