IWYU fix in service_worker_context_wrapper_unittest.cc.

BUG=546640
TBR=bashi@chromium.org

Change-Id: I3cf922b974fe5259962f50e2e5431900d2e3b9d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900989Reviewed-by: Greg Thompson <grt@chromium.org>
Commit-Queue: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712978}

content/browser/service_worker/service_worker_context_wrapper_unittest.cc

@@ -6,6 +6,7 @@
 
 #include <memory>
 
+#include "base/files/scoped_temp_dir.h"
 #include "base/run_loop.h"
 #include "base/test/bind_test_util.h"
 #include "content/browser/service_worker/service_worker_context_core.h"