Refactor PrefHashStore's BeginTransaction to take a rawptr

components/user_prefs/tracked/pref_hash_store.h

Index: components/user_prefs/tracked/pref_hash_store.h
diff --git a/components/user_prefs/tracked/pref_hash_store.h b/components/user_prefs/tracked/pref_hash_store.h
index 2fdc617301ae1fea64526ae16fe5d6621c272406..d50eac7954a0cf3b703e0505f0704779b91af51b 100644
--- a/components/user_prefs/tracked/pref_hash_store.h
+++ b/components/user_prefs/tracked/pref_hash_store.h
@@ -21,8 +21,10 @@ class PrefHashStore {
   // of operations on the hash store. |storage| MAY be used as the backing store
   // depending on the implementation. Therefore the HashStoreContents used for
   // related transactions should correspond to the same underlying data store.
+  // Does not own the HashStoreContents; callers must ensure transaction must
+  // not outlive |storage|.

[gab, 2016/09/01 20:31:50]

Raw pointer in Chromium always implies lack of ownership, last sentence could
simply be:

// |storage| must outlive the returned transaction.

[proberge, 2016/09/06 19:24:10]

Done.

   virtual std::unique_ptr<PrefHashStoreTransaction> BeginTransaction(
-      std::unique_ptr<HashStoreContents> storage) = 0;
+      HashStoreContents* storage) = 0;
 };
 
 #endif  // COMPONENTS_PREFS_TRACKED_PREF_HASH_STORE_H_