[Sync] Add keystore migration conflict support.

sync/internal_api/sync_encryption_handler_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sync/internal_api/sync_encryption_handler_impl.h"
 
 #include <queue>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 1086 matching lines @@
     if (passphrase_type_ != KEYSTORE_PASSPHRASE &&
         nigori.passphrase_type() ==
             sync_pb::NigoriSpecifics::KEYSTORE_PASSPHRASE) {
       return true;
     } else if (IsExplicitPassphrase(passphrase_type_) &&
                !encrypt_everything_) {
       return true;
     } else if (passphrase_type_ == KEYSTORE_PASSPHRASE &&
                encrypt_everything_) {
       return true;
+    } else if (
+        cryptographer.is_ready() &&
+        !cryptographer.CanDecryptUsingDefaultKey(nigori.encryption_keybag())) {
+      // We need to overwrite the keybag. This might involve overwriting the
+      // keystore decryptor too.
+      return true;
     } else {
       return false;
     }
   } else if (keystore_key_.empty()) {
     // If we haven't already migrated, we don't want to do anything unless
     // a keystore key is available (so that those clients without keystore
     // encryption enabled aren't forced into new states, e.g. frozen implicit
     // passphrase).
     return false;
   }
@@ skipping 24 matching lines @@
     DVLOG(1) << "Switching to frozen implicit passphrase due to already having "
              << "full encryption.";
     new_passphrase_type = FROZEN_IMPLICIT_PASSPHRASE;
     migrated_nigori.clear_keystore_decryptor_token();
   } else if (IsExplicitPassphrase(passphrase_type_)) {
     DVLOG_IF(1, !encrypt_everything_) << "Enabling encrypt everything due to "
                                       << "explicit passphrase";
     new_encrypt_everything = true;
     migrated_nigori.clear_keystore_decryptor_token();
   } else {
-    DCHECK_EQ(passphrase_type_, IMPLICIT_PASSPHRASE);
     DCHECK(!encrypt_everything_);
     new_passphrase_type = KEYSTORE_PASSPHRASE;
     DVLOG(1) << "Switching to keystore passphrase state.";
   }
   migrated_nigori.set_encrypt_everything(new_encrypt_everything);
   migrated_nigori.set_passphrase_type(
       EnumPassphraseTypeToProto(new_passphrase_type));
   migrated_nigori.set_keybag_is_frozen(true);
 
   if (!keystore_key_.empty()) {
@@ skipping 119 matching lines @@
           SyncEncryptionHandler::Observer,
           observers_,
           OnCryptographerStateChanged(cryptographer));
       return true;
     }
   }
   return false;
 }
 
 }  // namespace browser_sync