[Sync:USS] Implement GetKeystoreMigrationTime()

GetKeystoreMigrationTime() is a simple getter used for logging
purposes.

Bug: 922900
Change-Id: I6968a7eb7a315a1b4bbf2974ee2acfcda2d0bd67
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1814198
Commit-Queue: Maksim Moskvitin <mmoskvitin@google.com>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701236}

components/sync/nigori/nigori_sync_bridge_impl.cc

@@ -724,8 +724,7 @@ bool NigoriSyncBridgeImpl::IsEncryptEverythingEnabled() const {
 
 base::Time NigoriSyncBridgeImpl::GetKeystoreMigrationTime() const {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-  NOTIMPLEMENTED();
-  return base::Time();
+  return state_.keystore_migration_time;
 }
 
 KeystoreKeysHandler* NigoriSyncBridgeImpl::GetKeystoreKeysHandler() {

components/sync/nigori/nigori_sync_bridge_impl_unittest.cc

@@ -193,6 +193,7 @@ sync_pb::NigoriSpecifics BuildKeystoreNigoriSpecifics(
       specifics.mutable_keystore_decryptor_token()));
 
   specifics.set_passphrase_type(sync_pb::NigoriSpecifics::KEYSTORE_PASSPHRASE);
+  specifics.set_keystore_migration_time(TimeToProtoTime(base::Time::Now()));
   return specifics;
 }
 
@@ -394,6 +395,7 @@ TEST_F(NigoriSyncBridgeImplTest,
                                NotNull(), /*has_pending_keys=*/false));
   EXPECT_THAT(bridge()->MergeSyncData(std::move(entity_data)),
               Eq(base::nullopt));
+  EXPECT_THAT(bridge()->GetKeystoreMigrationTime(), Not(NullTime()));
 
   const Cryptographer& cryptographer = bridge()->GetCryptographerForTesting();
   EXPECT_THAT(cryptographer, CanDecryptWith(kKeystoreKeyParams));
@@ -497,12 +499,13 @@ TEST_F(NigoriSyncBridgeImplTest,
   EXPECT_THAT(bridge()->MergeSyncData(std::move(default_entity_data)),
               Eq(base::nullopt));
   EXPECT_THAT(bridge()->GetData(), HasKeystoreNigori());
+  EXPECT_THAT(bridge()->GetKeystoreMigrationTime(), Not(NullTime()));
+  EXPECT_EQ(bridge()->GetPassphraseTypeForTesting(),
+            sync_pb::NigoriSpecifics::KEYSTORE_PASSPHRASE);
 
   const Cryptographer& cryptographer = bridge()->GetCryptographerForTesting();
   EXPECT_THAT(cryptographer, CanDecryptWith(kKeystoreKeyParams));
   EXPECT_THAT(cryptographer, HasDefaultKeyDerivedFrom(kKeystoreKeyParams));
-  // TODO(crbug.com/922900): verify that passphrase type is equal to
-  // KeystorePassphrase once passphrase type support is implemented.
 }
 
 // Tests that we can perform initial sync with custom passphrase Nigori.