cros: Add UMA metrics in migration UI to get more information from migration failures.

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 968a9ebdc80e9087e03747f45ac68c50f9d07155..5dba39d5b924ece87fa9be9b2ac9750b5f46d4cd 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
@@ -47,14 +47,17 @@ class EncryptionMigrationScreenHandler : public EncryptionMigrationScreenView,
   void Initialize() override;
 
  private:
-  // Enumeration for the migration state. These values must be kept in sync with
-  // EncryptionMigrationUIState in JS code.
+  // Enumeration for migration UI state. These values must be kept in sync with
+  // EncryptionMigrationUIState in JS code, and match the numbering for
+  // MigrationUIScreen in histograms/enums.xml. Do not reorder or remove items,
+  // only add new items before COUNT.
   enum UIState {
     INITIAL = 0,
     READY = 1,
     MIGRATING = 2,
     MIGRATION_FAILED = 3,
     NOT_ENOUGH_STORAGE = 4,
+    COUNT
   };
 
   // WebUIMessageHandler implementation:
@@ -66,7 +69,8 @@ class EncryptionMigrationScreenHandler : public EncryptionMigrationScreenView,
   // Handlers for JS API callbacks.
   void HandleStartMigration();
   void HandleSkipMigration();
-  void HandleRequestRestart();
+  void HandleRequestRestartOnLowStorage();
+  void HandleRequestRestartOnFailure();
   void HandleOpenFeedbackDialog();
 
   // Updates UI state.
@@ -94,6 +98,9 @@ class EncryptionMigrationScreenHandler : public EncryptionMigrationScreenView,
                            uint64_t total);
   void OnMigrationRequested(bool success);
 
+  // Records UMA about visible screen after delay.
+  void OnDelayedRecordVisibleScreen(UIState state);
+
   Delegate* delegate_ = nullptr;
   bool show_on_init_ = false;