Cleanup PreferenceMACs on browser_tests startup

services/preferences/tracked/registry_hash_store_contents_win.h

 // Copyright 2016 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.
 
 #ifndef SERVICES_PREFERENCES_TRACKED_REGISTRY_HASH_STORE_CONTENTS_WIN_H_
 #define SERVICES_PREFERENCES_TRACKED_REGISTRY_HASH_STORE_CONTENTS_WIN_H_
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "services/preferences/tracked/hash_store_contents.h"
 
 // Implements HashStoreContents by storing MACs in the Windows registry.
 class RegistryHashStoreContentsWin : public HashStoreContents {
  public:
   // Constructs a RegistryHashStoreContents which acts on a registry entry
-  // defined by |registry_path| and |store_key|.
+  // defined by |registry_path| and |store_key|. If |store_key| begins with
+  // base::ScopedTempDir::GetTempDirPrefix(), this RegistryHashStoreContentsWin
+  // will self Reset() on destruction to avoid proliferating keys in tests that
+  // create a profile in a ScopedTempDir (https://crbug.com/721245).
   explicit RegistryHashStoreContentsWin(const base::string16& registry_path,
                                         const base::string16& store_key);
 
+  ~RegistryHashStoreContentsWin() override;
+
   // HashStoreContents overrides:
   bool IsCopyable() const override;
   std::unique_ptr<HashStoreContents> MakeCopy() const override;
   base::StringPiece GetUMASuffix() const override;
   void Reset() override;
   bool GetMac(const std::string& path, std::string* out_value) override;
   bool GetSplitMacs(const std::string& path,
                     std::map<std::string, std::string>* split_macs) override;
   void SetMac(const std::string& path, const std::string& value) override;
   void SetSplitMac(const std::string& path,
                    const std::string& split_path,
                    const std::string& value) override;
   bool RemoveEntry(const std::string& path) override;
 
   // Unsupported HashStoreContents overrides:
   void ImportEntry(const std::string& path,
                    const base::Value* in_value) override;
   const base::DictionaryValue* GetContents() const override;
   std::string GetSuperMac() const override;
   void SetSuperMac(const std::string& super_mac) override;
 
  private:
   // Helper constructor for |MakeCopy|.
   explicit RegistryHashStoreContentsWin(
       const RegistryHashStoreContentsWin& other);
 
   const base::string16 preference_key_name_;
+  const bool reset_on_delete_;
 };
 
 #endif  // SERVICES_PREFERENCES_TRACKED_REGISTRY_HASH_STORE_CONTENTS_WIN_H_