Copy the necessary build overrides from Chromium

gtest.gni

Index: gtest.gni
diff --git a/gtest.gni b/gtest.gni
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+# 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.
+
+# This file is based on Chromium's version in //build_overrides/gtest.gni
+# with the changes outlined below.
+
+# Exclude support for registering main function in multi-process tests.
+#
+# This value differs from Chromium's version as we do not currently use
+# multi-process tests in Native Client and this support requires additional
+# source files from Chromium codebase.
+gtest_include_multiprocess = false
+
+# Exclude support for platform-specific operations across unit tests.
+#
+# This value differs from Chromium's version as we do not currently support
+# platform-specific operations in Native Client and this support requires
+# additional source files from Chromium codebase.
+gtest_include_platform_test = false