[Sync] Persist keystore key across restarts

sync/util/cryptographer.h

Index: sync/util/cryptographer.h
diff --git a/sync/util/cryptographer.h b/sync/util/cryptographer.h
index 633a1d13638643b1720fa514eb5027eea6986e1f..c1fecf0bf4f21f098a264d826aaca12df5d55c49 100644
--- a/sync/util/cryptographer.h
+++ b/sync/util/cryptographer.h
@@ -99,6 +99,10 @@ class Cryptographer {
   // never call Bootstrap at all.
   void Bootstrap(const std::string& restored_bootstrap_token);
 
+  // Bootstrap the keystore key.
+  void BootstrapKeystoreKey(
+      const std::string& restored_keystore_bootstrap_token);
+
   // Returns whether we can decrypt |encrypted| using the keys we currently know
   // about.
   bool CanDecrypt(const sync_pb::EncryptedData& encrypted) const;
@@ -170,6 +174,9 @@ class Cryptographer {
   // can't be created (i.e. if this Cryptograhper doesn't have valid keys).
   bool GetBootstrapToken(std::string* token) const;
 
+  // Obtain the bootstrap token based on the keystore encryption key.
+  bool GetKeystoreKeyBootstrapToken(std::string* token) const;
+
   // Update the cryptographer based on the contents of the nigori specifics.
   // This updates both the encryption keys and the set of encrypted types.
   // Returns NEEDS_PASSPHRASE if was unable to decrypt the pending keys,
@@ -187,7 +194,7 @@ class Cryptographer {
 
   // Returns true if we currently have a keystore-derived nigori, false
   // otherwise.
-  bool HasKeystoreKey();
+  bool HasKeystoreKey() const;
 
   // The set of types that are always encrypted.
   static syncable::ModelTypeSet SensitiveTypes();