Update flatbuffers to HEAD of upstream

third_party/flatbuffers/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//testing/test.gni")
 import("//third_party/flatbuffers/flatbuffer.gni")
 
 config("flatbuffers_config") {
   include_dirs = [ "src/include" ]
 }
 
 source_set("flatbuffers") {
   sources = [
     "src/include/flatbuffers/flatbuffers.h",
     "src/include/flatbuffers/hash.h",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   public_configs = [ ":flatbuffers_config" ]
 }
 
 source_set("compiler_files") {
   sources = [
-    "src/include/idl.h",
-    "src/include/util.h",
+    "src/include/flatbuffers/code_generators.h",
+    "src/include/flatbuffers/idl.h",
+    "src/include/flatbuffers/util.h",
     "src/src/idl_gen_cpp.cpp",
     "src/src/idl_gen_fbs.cpp",
     "src/src/idl_gen_general.cpp",
     "src/src/idl_gen_go.cpp",
     "src/src/idl_gen_js.cpp",
     "src/src/idl_gen_php.cpp",
     "src/src/idl_gen_python.cpp",
     "src/src/idl_gen_text.cpp",
     "src/src/idl_parser.cpp",
     "src/src/reflection.cpp",
@@ skipping 43 matching lines @@
   ]
   deps = [
     ":compiler_files",
     ":flatbuffers",
     ":flatbuffers_samplebuffer",
   ]
   data = [
     "src/tests/",
   ]
 }