src/vs/workbench/browser/parts/editor/editorPart.ts/EditorPart/doCreateGridControlWithPreviousState
class EditorPart:	private doCreateGridControlWithPreviousState(): boolean {
		const uiState: IEditorPartUIState = this.workspaceMemento[EditorPart.EDITOR_PART_UI_STATE_STORAGE_KEY];
		if (uiState?.serializedGrid) {
			try {

				// MRU
				this.mostRecentActiveGroups = uiState.mostRecentActiveGroups;

				// Grid Widget
				this.doCreateGridControlWithState(uiState.serializedGrid, uiState.activeGroup);

				// Ensure last active group has focus
				this._activeGroup.focus();
			} catch (error) {

				// Log error
				onUnexpectedError(new Error(`Error restoring editor grid widget: ${error} (with state: ${JSON.stringify(uiState)})`));

				// Clear any state we have from the failing restore
				this.groupViews.forEach(group => group.dispose());
				this.groupViews.clear();
				this.mostRecentActiveGroups = [];

				return false; // failure
			}
		}

		return true; // success
	}