Multi-strategy based tracking.

chrome/browser/prefs/pref_hash_store.h

Index: chrome/browser/prefs/pref_hash_store.h
diff --git a/chrome/browser/prefs/pref_hash_store.h b/chrome/browser/prefs/pref_hash_store.h
index ebef8c0b2bceba521a763fc6a0e75ea3d2ec893e..a6f4f303b61c2739a6ad80b66e4b9406a9c70316 100644
--- a/chrome/browser/prefs/pref_hash_store.h
+++ b/chrome/browser/prefs/pref_hash_store.h
@@ -6,12 +6,12 @@
 #define CHROME_BROWSER_PREFS_PREF_HASH_STORE_H_
 
 #include <string>
+#include <vector>
 
 #include "base/memory/scoped_ptr.h"
 
-class PrefHashTracker;
-
 namespace base {
+class DictionaryValue;
 class Value;
 }  // namespace base
 
@@ -41,9 +41,24 @@ class PrefHashStore {
   virtual ValueState CheckValue(
       const std::string& path, const base::Value* initial_value) const = 0;
 
-  // Stores a hash of the current value of the preference at |path|.
+  // Stores a hash of the current |value| of the preference at |path|.
   virtual void StoreHash(const std::string& path,
                          const base::Value* value) = 0;
+
+  // Checks |initial_value| against the existing stored hashes for the split
+  // preference  at |path|. |invalid_keys| must initially be empty.

[Alexei Svitkine (slow), 2013/12/17 18:26:24]

Nit: Remove repeated space.

[gab, 2013/12/17 22:08:08]

Done.

+  // If the return value is CHANGED: |invalid_keys| will be filled with the keys

[Alexei Svitkine (slow), 2013/12/17 18:26:24]

Maybe document the valid return values here? (e.g. given that things like
CLEARED and MIGRATED shouldn't be returned by this).

[gab, 2013/12/17 22:08:08]

CLEARED can be return by this; it's when iteration over the items in the
dictionary in the implementation that CLEARED isn't expected, but this is an
implementation detail.

I don't think special documentation is otherwise required for MIGRATED here.

It currently never returns MIGRATED, but the callers shouldn't assume that.

+  // that are considered invalid (unknown or changed). |invalid_keys| will not
+  // be modified in all other cases.
+  virtual ValueState CheckSplitValue(
+      const std::string& path,
+      const base::DictionaryValue* initial_split_value,
+      std::vector<std::string>* invalid_keys) const = 0;
+
+  // Stores hashes for the |value| of the split preference at |path|.
+  virtual void StoreSplitHash(
+      const std::string& path,
+      const base::DictionaryValue* split_value) = 0;
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_HASH_STORE_H_