Make PassphraseType a "enum class" instead of "enum".

components/sync/test/fake_sync_encryption_handler.cc

Index: components/sync/test/fake_sync_encryption_handler.cc
diff --git a/components/sync/test/fake_sync_encryption_handler.cc b/components/sync/test/fake_sync_encryption_handler.cc
index 66bf7fb89938bcd0e6898be1f48421cbebebfcad..87b82660b8235d00922fa30e0491411a8d7d4e6d 100644
--- a/components/sync/test/fake_sync_encryption_handler.cc
+++ b/components/sync/test/fake_sync_encryption_handler.cc
@@ -12,7 +12,7 @@ namespace syncer {
 FakeSyncEncryptionHandler::FakeSyncEncryptionHandler()
     : encrypted_types_(SensitiveTypes()),
       encrypt_everything_(false),
-      passphrase_type_(IMPLICIT_PASSPHRASE),
+      passphrase_type_(PassphraseType::IMPLICIT_PASSPHRASE),
       cryptographer_(&encryptor_) {}
 FakeSyncEncryptionHandler::~FakeSyncEncryptionHandler() {}
 
@@ -28,7 +28,7 @@ void FakeSyncEncryptionHandler::ApplyNigoriUpdate(
   if (nigori.encrypt_everything())
     EnableEncryptEverything();
   if (nigori.keybag_is_frozen())
-    passphrase_type_ = CUSTOM_PASSPHRASE;
+    passphrase_type_ = PassphraseType::CUSTOM_PASSPHRASE;
 
   // TODO(zea): consider adding fake support for migration.
   if (cryptographer_.CanDecrypt(nigori.encryption_keybag()))
@@ -96,7 +96,7 @@ void FakeSyncEncryptionHandler::SetEncryptionPassphrase(
     const std::string& passphrase,
     bool is_explicit) {
   if (is_explicit)
-    passphrase_type_ = CUSTOM_PASSPHRASE;
+    passphrase_type_ = PassphraseType::CUSTOM_PASSPHRASE;
 }
 
 void FakeSyncEncryptionHandler::SetDecryptionPassphrase(