Update from https://crrev.com/312398

base/test/launcher/unit_test_launcher_ios.cc

Index: base/test/launcher/unit_test_launcher_ios.cc
diff --git a/base/test/launcher/unit_test_launcher_ios.cc b/base/test/launcher/unit_test_launcher_ios.cc
index d4276c89bccf0e1e8c4de3898f9ffc73807d68fe..acb6c71c498593de45db609262787928842c98ee 100644
--- a/base/test/launcher/unit_test_launcher_ios.cc
+++ b/base/test/launcher/unit_test_launcher_ios.cc
@@ -6,7 +6,9 @@
 
 #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"
 
@@ -27,6 +29,11 @@ int LaunchUnitTests(int argc,
       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();