feat(keys): add cross-host master key export (#599)

browser/browser.go

@@ -20,6 +20,7 @@ type Browser interface {
 	BrowserName() string
 	ProfileName() string
 	ProfileDir() string
+	UserDataDir() string
 	Extract(categories []types.Category) (*types.BrowserData, error)
 	CountEntries(categories []types.Category) (map[types.Category]int, error)
 }
@@ -114,6 +115,7 @@ func pickFromConfigs(configs []types.BrowserConfig, opts PickOptions) ([]Browser
 // KeyManager is implemented by engines that accept externally-provided master-key retrievers (Chromium family only).
 type KeyManager interface {
 	SetKeyRetrievers(keyretriever.Retrievers)
+	ExportKeys() (keyretriever.MasterKeys, error)
 }
 
 // KeychainPasswordReceiver is implemented by engines that need the macOS login password (Safari only).