PVer4: Test checksum on startup outside the hotpath of DB load

components/safe_browsing_db/v4_store.h

Index: components/safe_browsing_db/v4_store.h
diff --git a/components/safe_browsing_db/v4_store.h b/components/safe_browsing_db/v4_store.h
index d4559780cae063ccfeae55d8a14f29f33bff8082..457a995eb525ff13d5a4d48cfe3ffec5e0e2b3a5 100644
--- a/components/safe_browsing_db/v4_store.h
+++ b/components/safe_browsing_db/v4_store.h
@@ -246,6 +246,7 @@ class V4Store {
   FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestAdditionsWithRiceEncodingSucceeds);
   FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestRemovalsWithRiceEncodingSucceeds);
   FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestMergeUpdatesFailsChecksum);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestChecksumErrorOnStartup);
   friend class V4StoreTest;
 
   // If |prefix_size| is within expected range, and |raw_hashes_length| is a
@@ -299,8 +300,9 @@ class V4Store {
   // Merges the prefix map from the old store (|old_hash_prefix_map|) and the
   // update (additions_map) to populate the prefix map for the current store.
   // The indices in the |raw_removals| list, which may be NULL, are not merged.
-  // The SHA256 checksum of the final list of hash prefixes, in lexographically
-  // sorted order, must match |expected_checksum| (if it's not empty).
+  // The SHA256 checksum of the final list of hash prefixes, in
+  // lexicographically sorted order, must match |expected_checksum| (if it's not
+  // empty).
   ApplyUpdateResult MergeUpdate(const HashPrefixMap& old_hash_prefix_map,
                                 const HashPrefixMap& additions_map,
                                 const ::google::protobuf::RepeatedField<
@@ -341,6 +343,12 @@ class V4Store {
   // for the failure or reports success.
   StoreReadResult ReadFromDisk();
 
+  // Scheduled when reading the store file from disk on startup. When run, it
+  // ensures that the checksum of the hash prefixes in lexicographical sorted
+  // order matches the expected value. If not, it clears out the contents of
+  // the store.
+  void VerifyChecksum(const std::string& expected_checksum);
+
   // Writes the FULL_UPDATE |response| to disk as a V4StoreFileFormat proto.
   StoreWriteResult WriteToDisk(
       std::unique_ptr<ListUpdateResponse> response) const;