Update FlatBuffers to version 1.5.0.

third_party/flatbuffers/BUILD.gn

Index: third_party/flatbuffers/BUILD.gn
diff --git a/third_party/flatbuffers/BUILD.gn b/third_party/flatbuffers/BUILD.gn
index a6dc8f42ec8533f61ff45f9163bc5841d0e44d26..5a6e8f5c89090a1a50850aec3ef2c1b689d382c9 100644
--- a/third_party/flatbuffers/BUILD.gn
+++ b/third_party/flatbuffers/BUILD.gn
@@ -7,6 +7,9 @@ import("//third_party/flatbuffers/flatbuffer.gni")
 
 config("flatbuffers_config") {
   include_dirs = [ "src/include" ]
+
+  # This is to fix crbug.com/699958.
+  defines = [ "FLATBUFFERS_CPP98_STL" ]
 }
 
 source_set("flatbuffers") {
@@ -21,7 +24,13 @@ source_set("flatbuffers") {
 }
 
 source_set("compiler_files") {
+  include_dirs = [ "src/grpc" ]
   sources = [
+    "src/grpc/src/compiler/cpp_generator.cc",
+    "src/grpc/src/compiler/cpp_generator.h",
+    "src/grpc/src/compiler/go_generator.cc",
+    "src/grpc/src/compiler/go_generator.h",
+    "src/grpc/src/compiler/schema_interface.h",
     "src/include/flatbuffers/code_generators.h",
     "src/include/flatbuffers/idl.h",
     "src/include/flatbuffers/util.h",
@@ -29,6 +38,7 @@ source_set("compiler_files") {
     "src/src/idl_gen_fbs.cpp",
     "src/src/idl_gen_general.cpp",
     "src/src/idl_gen_go.cpp",
+    "src/src/idl_gen_grpc.cpp",
     "src/src/idl_gen_js.cpp",
     "src/src/idl_gen_php.cpp",
     "src/src/idl_gen_python.cpp",
@@ -78,6 +88,8 @@ test("flatbuffers_unittest") {
 
     # This is the actual test.
     "src/tests/test.cpp",
+
+    # TODO(pkalinnikov): Add "grpc/tests/grpctest.cpp" as well.

[engedy, 2017/03/09 17:39:32]

nit: Could you please reference https://crbug.com/NNNNNN here?

   ]
   deps = [
     ":compiler_files",
@@ -87,4 +99,5 @@ test("flatbuffers_unittest") {
   data = [
     "src/tests/",
   ]
+  defines = [ "FLATBUFFERS_TRACK_VERIFIER_BUFFER_SIZE" ]
 }