Support excluding Google Test extensions

GN build of Google Test including Chromium's extensions which make it
impossible to reuse the GN build definition outside of Chromium without
pulling the entire src/testing. We provide a way to exclude these
extensions from the build.

Review URL: https://codereview.chromium.org/1901313002

Cr-Original-Commit-Position: refs/heads/master@{#388400}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: ccff0d0ca88dc927380c9d0d4315af5faeee626d

secondary/testing/gtest/BUILD.gn

@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build_overrides/gtest.gni")
+
 config("gtest_config") {
   visibility = [
     ":*",
@@ -91,9 +93,6 @@ static_library("gtest") {
     "include/gtest/internal/gtest-type-util.h",
 
     #"gtest/src/gtest-all.cc",  # Not needed by our build.
-    "../multiprocess_func_list.cc",
-    "../multiprocess_func_list.h",
-    "../platform_test.h",
     "src/gtest-death-test.cc",
     "src/gtest-filepath.cc",
     "src/gtest-internal-inl.h",
@@ -104,6 +103,17 @@ static_library("gtest") {
     "src/gtest.cc",
   ]
 
+  if (gtest_include_multiprocess) {
+    sources += [
+      "../multiprocess_func_list.cc",
+      "../multiprocess_func_list.h",
+    ]
+  }
+
+  if (gtest_include_platform_test) {
+    sources += [ "../platform_test.h" ]
+  }
+
   if (is_mac || is_ios) {
     if (is_ios) {
       set_sources_assignment_filter([])
@@ -111,8 +121,10 @@ static_library("gtest") {
     sources += [
       "../gtest_mac.h",
       "../gtest_mac.mm",
-      "../platform_test_mac.mm",
     ]
+    if (gtest_include_platform_test) {
+      sources += [ "../platform_test_mac.mm" ]
+    }
     set_sources_assignment_filter(sources_assignment_filter)
   }