Inject the custom InitGoogleTest function using a macro.

src/gtest.cc

@@ -5361,13 +5361,21 @@ void InitGoogleTestImpl(int* argc, CharType** argv) {
 //
 // Calling the function for the second time has no user-visible effect.
 void InitGoogleTest(int* argc, char** argv) {
+#if defined(GTEST_CUSTOM_INIT_GOOGLE_TEST_FUNCTION_)
+  GTEST_CUSTOM_INIT_GOOGLE_TEST_FUNCTION_(argc, argv);
+#else  // defined(GTEST_CUSTOM_INIT_GOOGLE_TEST_FUNCTION_)
   internal::InitGoogleTestImpl(argc, argv);
+#endif  // defined(GTEST_CUSTOM_INIT_GOOGLE_TEST_FUNCTION_)
 }
 
 // This overloaded version can be used in Windows programs compiled in
 // UNICODE mode.
 void InitGoogleTest(int* argc, wchar_t** argv) {
+#if defined(GTEST_CUSTOM_INIT_GOOGLE_TEST_FUNCTION_)
+  GTEST_CUSTOM_INIT_GOOGLE_TEST_FUNCTION_(argc, argv);
+#else  // defined(GTEST_CUSTOM_INIT_GOOGLE_TEST_FUNCTION_)
   internal::InitGoogleTestImpl(argc, argv);
+#endif  // defined(GTEST_CUSTOM_INIT_GOOGLE_TEST_FUNCTION_)
 }
 
 }  // namespace testing