Integrate registry_hash_store_contents with the rest of tracked prefs.

components/user_prefs/tracked/hash_store_contents.h

 // 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.
 
 #ifndef COMPONENTS_USER_PREFS_TRACKED_HASH_STORE_CONTENTS_H_
 #define COMPONENTS_USER_PREFS_TRACKED_HASH_STORE_CONTENTS_H_
 
 #include <map>
 #include <memory>
 #include <string>
 
 namespace base {
 class DictionaryValue;
 class Value;
 }  // namespace base
 
+enum class HashStoreContentsType : int32_t {

[gab, 2016/08/08 04:37:45]

Can get rid of this now?

[proberge, 2016/08/31 17:30:16]

Done.

+  DICTIONARY_HASH_STORE_CONTENTS = 1,
+  REGISTRY_HASH_STORE_CONTENTS = 2
+};
+
 // Provides access to the contents of a preference hash store. The store
 // contains the following data:
 // Contents: a client-defined dictionary that should map preference names to
 // MACs.
 // Version: a client-defined version number for the format of Contents.
 // Super MAC: a MAC that authenticates the entirety of Contents.
 class HashStoreContents {
  public:
   virtual ~HashStoreContents() {}
 
+  // Helper function to make a clone of this object.
+  // NOTE: this is intended to be used as a lightweight alternative to making
+  // this class RefCountedThreadSafe. Do not make copies of this object unless
+  // you can't avoid it.

[gab, 2016/08/08 04:37:45]

In order to make this API cleaner, I'd like us to add

// Returns true if this implementation of HashStoreContents can be copied via
MakeCopy().
virtual bool IsCopyable() const = 0;

and then I think we can make the documentation of MakeCopy():

// Returns a copy of this HashStoreContents. Must only be called on lightweight
implementations (which return true from IsCopyable()) and only in scenarios
where a copy cannot be avoided.

(note lack of use of "you"/"we" pronouns in comment too which is preferred)

[proberge, 2016/08/31 17:30:16]

Done.

+  virtual std::unique_ptr<HashStoreContents> MakeCopy() const = 0;
+
+  // Returns the string to append to UMA histograms for this store type.

[gab, 2016/08/08 04:37:45]

"Returns the suffix to be appended"

(the fact that it's a string is implicit IMO)

[proberge, 2016/08/31 17:30:16]

Done.

+  // The returned value must either be an empty string or one of the values in
+  // histograms.xml's TrackedPreferencesExternalValidators.
+  virtual std::string GetUMASuffix() const = 0;

[gab, 2016/08/08 04:37:45]

Return a base::StringPiece instead of an std::string to avoid forming a string
out of constants (i.e. avoid a copy).

[proberge, 2016/08/31 17:30:16]

Done.

+
   // Discards all data related to this hash store.
   virtual void Reset() = 0;
 
   // Outputs the MAC validating the preference at path. Returns true if a MAC
   // was successfully read and false otherwise.
   virtual bool GetMac(const std::string& path, std::string* out_value) = 0;
 
   // Outputs the MACS validating the split preference at path. Returns true if
   // MACS were successfully read and false otherwise.
   virtual bool GetSplitMacs(const std::string& path,
@@ skipping 28 matching lines @@
   // Retrieves the super MAC value previously stored by SetSuperMac. May be
   // empty if no super MAC has been stored or if this store does not support
   // super MACs.
   virtual std::string GetSuperMac() const = 0;
 
   // Stores a super MAC value for this hash store.
   virtual void SetSuperMac(const std::string& super_mac) = 0;
 };
 
 #endif  // COMPONENTS_USER_PREFS_TRACKED_HASH_STORE_CONTENTS_H_