Use the /WX flag to have link warnings treated as errors.

media/mojo/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("//testing/test.gni")
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "clients/mojo_audio_decoder_unittest.cc",
@@ skipping 17 matching lines @@
     "//media/mojo/interfaces",
     "//media/mojo/services:lib",
     "//services/service_manager/tests:interfaces",
     "//testing/gmock",
     "//testing/gtest",
     "//ui/gfx:test_support",
   ]
 }
 
 test("media_mojo_unittests") {
+  # crbug.com/676418: Suppress symbol import warnings.
+  if (is_win && is_component_build) {
+    ldflags = [
+      "/ignore:4217",
+      "/ignore:4049",
+    ]
+  }
+
   deps = [
     ":unit_tests",
     "//mojo/edk/test:run_all_unittests",
   ]
 }