Make sure that when a SupportsUserData is destroyed, objects destroyed transitively see it as empty.

base/supports_user_data_unittest.cc

+// Copyright 2014 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/supports_user_data.h"
+
+#include <vector>
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+namespace {
+
+struct TestSupportsUserData : public SupportsUserData {};
+
+struct UsesItself : public SupportsUserData::Data {
+  UsesItself(SupportsUserData* supports_user_data, const void* key)
+      : supports_user_data_(supports_user_data), key_(key) {}

[Peter Kasting, 2014/05/28 03:44:13]

Nit: One initializer per line if they don't all fit on the same line as the
function name

[Jeffrey Yasskin, 2014/05/28 05:45:26]

Done, and filed b/15292387.

+  virtual ~UsesItself() {
+    EXPECT_EQ(NULL, supports_user_data_->GetUserData(key_));
+  }
+
+  SupportsUserData* supports_user_data_;
+  const void* key_;
+};
+
+TEST(SupportsUserDataTest, ClearWorksRecursively) {
+  TestSupportsUserData supports_user_data;
+  char key = 0;
+  supports_user_data.SetUserData(&key,
+                                 new UsesItself(&supports_user_data, &key));
+  // Destruction of supports_user_data runs the actual test.
+}
+
+}  // namespace
+}  // namespace base

[Peter Kasting, 2014/05/28 03:44:13]

Nit: Either add a blank line here or take it out above

(Though probably I'd just remove the anonymous namespace, it doesn't seem
important for a test)

[Jeffrey Yasskin, 2014/05/28 05:45:26]

Thanks; I've taken it out above.
It's especially important in a test, where we'd like to use short names for
helper classes, but we really don't want multiple tests to use the same name as
each other, lest the ODR bite us.