[Protobuf] Add <map> include to workaround a gcc bug

GCC gets a bit confused by libc++'s map headers, and including <map>
after <set> can cause problems under certain conditions [1].

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81347

BUG=webrtc:7922
R=pkasting@chromium.org,dpranke@chromium.org

Review-Url: https://codereview.chromium.org/2974603002
Cr-Commit-Position: refs/heads/master@{#486608}

third_party/protobuf/README.chromium

@@ -86,3 +86,7 @@ Description of the patches:
   removed in C++11 mode.
 
   Fixed in https://github.com/google/protobuf/pull/1549
+
+- 0012-add-map-include.patch
+
+  Workaround for gcc bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81347

third_party/protobuf/patches/0012-add-map-include.patch

+diff -ru protobuf2/src/google/protobuf/descriptor.h protobuf/src/google/protobuf/descriptor.h
+--- protobuf2/src/google/protobuf/descriptor.h	2017-07-06 15:32:27.892104861 -0700
++++ protobuf/src/google/protobuf/descriptor.h	2017-07-06 15:19:07.042709476 -0700
+@@ -54,6 +54,7 @@
+ #ifndef GOOGLE_PROTOBUF_DESCRIPTOR_H__
+ #define GOOGLE_PROTOBUF_DESCRIPTOR_H__
+ 
++#include <map>
+ #include <memory>
+ #ifndef _SHARED_PTR_H
+ #include <google/protobuf/stubs/shared_ptr.h>

third_party/protobuf/src/google/protobuf/descriptor.h

@@ -54,6 +54,7 @@
 #ifndef GOOGLE_PROTOBUF_DESCRIPTOR_H__
 #define GOOGLE_PROTOBUF_DESCRIPTOR_H__
 
+#include <map>
 #include <memory>
 #ifndef _SHARED_PTR_H
 #include <google/protobuf/stubs/shared_ptr.h>

tools/mb/mb.py

@@ -9,6 +9,10 @@ MB is a wrapper script for GYP and GN that can be used to generate build files
 for sets of canned configurations and analyze them.
 """
 
+# TODO(thomasanderson): Remove this comment.  It is added to
+# workaround https://crbug.com/736215 for CL
+# https://codereview.chromium.org/2974603002/
+
 from __future__ import print_function
 
 import argparse