Multi-strategy based tracking.

chrome/browser/prefs/pref_hash_store_impl.cc

 // Copyright 2013 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 "chrome/browser/prefs/pref_hash_store_impl.h"
 
 #include "base/logging.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
@@ skipping 50 matching lines @@
   // Get the dictionary corresponding to the profile name, which may have a '.'
   if (!update->GetDictionaryWithoutPathExpansion(hash_store_id_,
                                                  &child_dictionary)) {
     child_dictionary = new DictionaryValue;
     update->SetWithoutPathExpansion(hash_store_id_, child_dictionary);
   }
 
   child_dictionary->SetString(
       path, pref_hash_calculator_.Calculate(path, new_value));
 }
+
+PrefHashStore::ValueState PrefHashStoreImpl::CheckSplitValue(
+    const std::string& path,
+    const base::DictionaryValue* initial_split_value,
+    std::vector<std::string>* invalid_keys) const {
+  DCHECK(invalid_keys && invalid_keys->empty());
+
+  bool has_hashes = HasPath(path);
+
+  // Treat NULL and empty the same; otherwise we would need to store a hash
+  // for the entire dictionary (or some other special beacon) to
+  // differentiate these two cases which are really the same for
+  // dictionaries.
+  if (!initial_split_value || initial_split_value->empty())
+    return has_hashes ? CLEARED : UNCHANGED;
+
+  if (!has_hashes)
+    return UNKNOWN_VALUE;
+
+  for (base::DictionaryValue::Iterator it(*initial_split_value); !it.IsAtEnd();
+       it.Advance()) {
+    ValueState value_state = CheckValue(path + "." + it.key(), &it.value());
+    switch (value_state) {
+      case CLEARED:  // Falls through.

[erikwright (departed), 2013/12/17 02:22:50]

Don't fall through, have a dedicated NOTREACHED for less ambiguity. Especially
with the long comment separating this from the next case.

[gab, 2013/12/17 18:08:05]

Done.

+        // CLEARED doesn't make sense as a NULL value would never be sampled
+        // by the DictionaryValue::Iterator; in fact it is a known weakness of
+        // this current algorithm to not detect the case where a single key is
+        // cleared entirely from the dictionary pref.
+      case MIGRATED:
+        // Split tracked preferences were introduced after the migration started
+        // so no migration is expected.
+        NOTREACHED();
+        break;
+      case UNCHANGED:
+        break;
+      case CHANGED:  // Falls through.
+      case UNKNOWN_VALUE:
+        // Declare this value invalid, whether it was changed or never seen
+        // before.
+        invalid_keys->push_back(it.key());
+        break;
+    }
+  }
+  return invalid_keys->empty() ? UNCHANGED : CHANGED;
+}
+
+void PrefHashStoreImpl::StoreSplitHash(
+    const std::string& path,
+    const base::DictionaryValue* split_value) {
+  ClearPath(path);
+
+  if (split_value) {
+    for (base::DictionaryValue::Iterator it(*split_value); !it.IsAtEnd();
+         it.Advance()) {
+      StoreHash(path + "." + it.key(), &it.value());
+    }
+  }
+}
+
+void PrefHashStoreImpl::ClearPath(const std::string& path) {
+  DictionaryPrefUpdate update(local_state_, prefs::kProfilePreferenceHashes);
+  DictionaryValue* child_dictionary = NULL;
+
+  if (update->GetDictionaryWithoutPathExpansion(hash_store_id_,
+                                                &child_dictionary)) {
+    child_dictionary->Remove(path, NULL);
+  }
+}
+
+bool PrefHashStoreImpl::HasPath(const std::string& path) const {
+  const base::DictionaryValue* pref_hash_dicts =
+      local_state_->GetDictionary(prefs::kProfilePreferenceHashes);
+  const base::DictionaryValue* hashed_prefs = NULL;
+  pref_hash_dicts->GetDictionaryWithoutPathExpansion(hash_store_id_,
+                                                     &hashed_prefs);
+  return hashed_prefs && hashed_prefs->Get(path, NULL);
+}