[Sync] Add ability to save/restore Nigori to SyncEncryptionHandlerImpl

SyncEncryptionHandlerImpl now detects when a user enables passphrase
encryption locally and notifies observers with the updated Nigori
state. An observer can then use this state to restore a future instance
of SyncEncryptionHandler. The ability to save/restore Nigori across
Directory instances is a prerequisite for issuing a lightweight
"dashboard stop and clear" when a user enables passphrase encryption.

Add OnLocalSetCustomPassphrase to SyncEncryptionHandler interface.

Plumb OnLocalSetCustomPassphrase events from SyncEncryptionHandlerImpl
on the sync thread to ProfileSyncService on the UI thread.

Loosen a restriction on ModelNeutralMutableEntry's capabilities.

BUG=490836

Review URL: https://codereview.chromium.org/1177853002

Cr-Commit-Position: refs/heads/master@{#334513}

1 files changed, 12 insertions, 1 deletions

diff --git a/sync/internal_api/sync_encryption_handler_impl.h b/sync/internal_api/sync_encryption_handler_impl.h
index 79f43f2..4e466f1 100644
--- a/sync/internal_api/sync_encryption_handler_impl.h
+++ b/sync/internal_api/sync_encryption_handler_impl.h
@@ -88,6 +88,11 @@ class SYNC_EXPORT_PRIVATE SyncEncryptionHandlerImpl
   base::Time migration_time() const;
   base::Time custom_passphrase_time() const;
 
+  // Restore a saved nigori obtained from OnLocalSetPassphraseEncryption.
+  //
+  // Writes the nigori to the Directory and updates the Cryptographer.
+  void RestoreNigori(const SyncEncryptionHandler::NigoriState& nigori_state);
+
  private:
   friend class SyncEncryptionHandlerImplTest;
   FRIEND_TEST_ALL_PREFIXES(SyncEncryptionHandlerImplTest,
@@ -139,7 +144,10 @@ class SYNC_EXPORT_PRIVATE SyncEncryptionHandlerImpl
   // Iterate over all encrypted types ensuring each entry is properly encrypted.
   void ReEncryptEverything(WriteTransaction* trans);
 
-  // Apply a nigori update. Updates internal and cryptographer state.
+  // Updates internal and cryptographer state.
+  //
+  // Assumes |nigori| is already present in the Sync Directory.
+  //
   // Returns true on success, false if |nigori| was incompatible, and the
   // nigori node must be corrected.
   // Note: must be called from within a transaction.
@@ -261,6 +269,9 @@ class SYNC_EXPORT_PRIVATE SyncEncryptionHandlerImpl
   // (if known). Else return base::Time().
   base::Time GetExplicitPassphraseTime() const;
 
+  // Notify observers when a custom passphrase is set by this device.
+  void NotifyObserversOfLocalCustomPassphrase(WriteTransaction* trans);
+
   base::ThreadChecker thread_checker_;
 
   base::ObserverList<SyncEncryptionHandler::Observer> observers_;