Go bindings: Change generated enum value constants to be typed as the enum type.

mojo/go/BUILD.gn

 # Copyright 2014 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("rules.gni")
 
 go_library("application") {
   sources = [
     "//mojo/public/go/application/application_impl.go",
     "//mojo/public/go/application/connection.go",
@@ skipping 48 matching lines @@
     testonly = true
     deps = [
       ":system_test",
     ]
   }
   go_test_binary("system_test") {
     sources = [
       "tests/application_impl_test.go",
       "tests/async_waiter_test.go",
       "tests/encoding_test.go",
+      "tests/enums_test.go",
       "tests/interface_test.go",
       "tests/message_test.go",
       "tests/regression_test.go",
       "tests/request_response_test.go",
       "tests/router_test.go",
       "tests/system_test.go",
       "tests/testutil.go",
       "tests/testutil_test.go",
       "tests/union_test.go",
       "tests/validation_test.go",
       "tests/validation_type_test.go",
     ]
     static_library_sources = [
       "c_embedder/c_embedder.cc",
       "c_embedder/c_embedder.h",
     ]
     deps = [
       ":application",
       ":platform_cgo",
       "//examples/echo",
       "//mojo/edk/base_edk",
       "//mojo/edk/system",
       "//mojo/public/interfaces/bindings/tests:test_interfaces",
     ]
   }
 }