Make SafeBrowsingDatabase's PrefixSets only updatable by swapping a new one in.

chrome/browser/safe_browsing/safe_browsing_database.cc

Index: chrome/browser/safe_browsing/safe_browsing_database.cc
diff --git a/chrome/browser/safe_browsing/safe_browsing_database.cc b/chrome/browser/safe_browsing/safe_browsing_database.cc
index a5de866781858abc3bc049c2e7a463f3dd214ea3..2537959bd2a13584004a0f7670e9a323a597f5bf 100644
--- a/chrome/browser/safe_browsing/safe_browsing_database.cc
+++ b/chrome/browser/safe_browsing/safe_browsing_database.cc
@@ -696,7 +696,7 @@ bool SafeBrowsingDatabaseNew::ContainsUnwantedSoftwareUrl(
 
 bool SafeBrowsingDatabaseNew::PrefixSetContainsUrl(
     const GURL& url,
-    scoped_ptr<safe_browsing::PrefixSet>* prefix_set_getter,
+    scoped_ptr<const safe_browsing::PrefixSet>* prefix_set_getter,
     std::vector<SBPrefix>* prefix_hits,
     std::vector<SBFullHashResult>* cache_hits) {
   // This method is theoretically thread-safe but document that it is currently
@@ -726,7 +726,7 @@ bool SafeBrowsingDatabaseNew::ContainsBrowseUrlHashesForTesting(
 
 bool SafeBrowsingDatabaseNew::PrefixSetContainsUrlHashes(
     const std::vector<SBFullHash>& full_hashes,
-    scoped_ptr<safe_browsing::PrefixSet>* prefix_set_getter,
+    scoped_ptr<const safe_browsing::PrefixSet>* prefix_set_getter,
     std::vector<SBPrefix>* prefix_hits,
     std::vector<SBFullHashResult>* cache_hits) {
   // This method is theoretically thread-safe but document that it is currently
@@ -743,7 +743,7 @@ bool SafeBrowsingDatabaseNew::PrefixSetContainsUrlHashes(
   // |prefix_set_getter| can only be accessed while holding |lookup_lock_| hence
   // why it is passed as a parameter rather than passing the |prefix_set|
   // directly.
-  safe_browsing::PrefixSet* prefix_set = prefix_set_getter->get();
+  const safe_browsing::PrefixSet* prefix_set = prefix_set_getter->get();
   if (!prefix_set)
     return false;
 
@@ -1330,7 +1330,7 @@ int64 SafeBrowsingDatabaseNew::UpdateHashPrefixStore(
 void SafeBrowsingDatabaseNew::UpdatePrefixSetUrlStore(
     const base::FilePath& db_filename,
     SafeBrowsingStore* url_store,
-    scoped_ptr<safe_browsing::PrefixSet>* prefix_set,
+    scoped_ptr<const safe_browsing::PrefixSet>* prefix_set,
     FailureType finish_failure_type,
     FailureType write_failure_type) {
   DCHECK(thread_checker_.CalledOnValidThread());
@@ -1369,7 +1369,7 @@ void SafeBrowsingDatabaseNew::UpdatePrefixSetUrlStore(
     full_hash_results.push_back(add_full_hashes[i].full_hash);
   }
 
-  scoped_ptr<safe_browsing::PrefixSet> new_prefix_set(
+  scoped_ptr<const safe_browsing::PrefixSet> new_prefix_set(
       builder.GetPrefixSet(full_hash_results));
 
   // Swap in the newly built filter.
@@ -1382,8 +1382,6 @@ void SafeBrowsingDatabaseNew::UpdatePrefixSetUrlStore(
 
   // Persist the prefix set to disk. Note: there is no need to lock since the
   // only write to |*prefix_set| is on this thread (in the swap() above).
-  // TODO(gab): Strengthen this requirement by design (const pointers) rather
-  // than assumptions.
   WritePrefixSet(db_filename, prefix_set->get(), write_failure_type);
 
   // Gather statistics.
@@ -1422,13 +1420,13 @@ void SafeBrowsingDatabaseNew::UpdateSideEffectFreeWhitelistStore() {
     RecordFailure(FAILURE_SIDE_EFFECT_FREE_WHITELIST_UPDATE_FINISH);
     return;
   }
-  scoped_ptr<safe_browsing::PrefixSet>
-      prefix_set(builder.GetPrefixSetNoHashes());
+  scoped_ptr<const safe_browsing::PrefixSet> new_prefix_set(
+      builder.GetPrefixSetNoHashes());
 
   // Swap in the newly built prefix set.
   {
     base::AutoLock locked(lookup_lock_);
-    side_effect_free_whitelist_prefix_set_.swap(prefix_set);
+    side_effect_free_whitelist_prefix_set_.swap(new_prefix_set);
   }
 
   const base::FilePath side_effect_free_whitelist_filename =
@@ -1511,7 +1509,7 @@ void SafeBrowsingDatabaseNew::OnHandleCorruptDatabase() {
 // real error-handling.
 void SafeBrowsingDatabaseNew::LoadPrefixSet(
     const base::FilePath& db_filename,
-    scoped_ptr<safe_browsing::PrefixSet>* prefix_set,
+    scoped_ptr<const safe_browsing::PrefixSet>* prefix_set,
     FailureType read_failure_type) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
@@ -1622,7 +1620,7 @@ bool SafeBrowsingDatabaseNew::Delete() {
 
 void SafeBrowsingDatabaseNew::WritePrefixSet(
     const base::FilePath& db_filename,
-    safe_browsing::PrefixSet* prefix_set,
+    const safe_browsing::PrefixSet* prefix_set,
     FailureType write_failure_type) {
   DCHECK(thread_checker_.CalledOnValidThread());