Implement a basic UI flow for cryptohome encryption migration.

chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h

Index: chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h
diff --git a/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h b/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h
index 4ae2a93a032d00d45fd7be6c265a580912642cd3..6949c0b935540b1b21ffa0f48d420231fb4969d6 100644
--- a/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h
+++ b/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.h
@@ -8,6 +8,8 @@
 #include "base/macros.h"
 #include "chrome/browser/chromeos/login/screens/encryption_migration_screen_view.h"
 #include "chrome/browser/ui/webui/chromeos/login/base_screen_handler.h"
+#include "chromeos/login/auth/user_context.h"
+#include "third_party/cros_system_api/dbus/cryptohome/dbus-constants.h"
 
 namespace chromeos {
 
@@ -18,20 +20,58 @@ class EncryptionMigrationScreenHandler : public EncryptionMigrationScreenView,
   EncryptionMigrationScreenHandler();
   ~EncryptionMigrationScreenHandler() override;
 
-  // EncryptionMigrationScreenView:
+  // EncryptionMigrationScreenView implementation:
   void Show() override;
   void Hide() override;
   void SetDelegate(Delegate* delegate) override;
+  void SetUserContext(const UserContext& user_context) override;
 
-  // BaseScreenHandler:
+  // BaseScreenHandler implementation:
   void DeclareLocalizedValues(
       ::login::LocalizedValuesBuilder* builder) override;
   void Initialize() override;
 
  private:
+  // Enumeration for the migration state. These values must be kept in sync with
+  // EncryptionMigrationUIState in JS code.
+  enum UIState {
+    INITIAL = 0,
+    MIGRATING = 1,
+    MIGRATION_SUCCEEDED = 2,
+    MIGRATION_FAILED = 3
+  };
+
+  // WebUIMessageHandler implementation:
+  void RegisterMessages() override;
+
+  // Handlers for JS API callbacks.
+  void HandleStartMigration();
+  void HandleRequestRestart();
+
+  // Updates UI state.
+  void UpdateUIState(UIState state);
+
+  // Requests cryptohome to start encryption migration.
+  void StartMigration();
+
+  // Handlers for cryptohome API callbacks.
+  void OnMigrationProgress(cryptohome::DircryptoMigrationStatus status,
+                           uint64_t current,
+                           uint64_t total);
+  void OnMigrationRequested(bool success);
+
   Delegate* delegate_ = nullptr;
   bool show_on_init_ = false;
 
+  // The current UI state which should be refrected in the web UI.
+  UIState current_ui_state_ = INITIAL;
+
+  // The current user's UserContext, which is used to request the migration to
+  // cryptohome.
+  UserContext user_context_;
+
+  base::WeakPtrFactory<EncryptionMigrationScreenHandler> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(EncryptionMigrationScreenHandler);
 };