Update from https://crrev.com/312398

base/test/launcher/unit_test_launcher_ios.cc

 // Copyright 2013 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.
 
 #include "base/test/launcher/unit_test_launcher.h"
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
+#include "base/files/file_util.h"
 #include "base/logging.h"
+#include "base/mac/foundation_util.h"
 #include "base/test/gtest_util.h"
 #include "base/test/test_switches.h"
 
 namespace base {
 
 int LaunchUnitTests(int argc,
                     char** argv,
                     const RunTestSuiteCallback& run_test_suite) {
   CHECK(CommandLine::InitializedForCurrentProcess() ||
         CommandLine::Init(argc, argv));
   const CommandLine* command_line = CommandLine::ForCurrentProcess();
   if (command_line->HasSwitch(switches::kTestLauncherListTests)) {
     FilePath list_path(command_line->GetSwitchValuePath(
         switches::kTestLauncherListTests));
     if (WriteCompiledInTestsToFile(list_path)) {
       return 0;
     } else {
       LOG(ERROR) << "Failed to write list of tests.";
       return 1;
     }
+  } else if (command_line->HasSwitch(
+                 switches::kTestLauncherPrintWritablePath)) {
+    fprintf(stdout, "%s", mac::GetUserLibraryPath().value().c_str());
+    fflush(stdout);
+    return 0;
   }
 
   return run_test_suite.Run();
 }
 
 }  // namespace base