src/vs/workbench/browser/parts/editor/editorPane.ts/EditorMemento/loadEditorState
class EditorMemento:	loadEditorState(group: IEditorGroup, resourceOrEditor: URI | EditorInput): T | undefined {
		const resource = this.doGetResource(resourceOrEditor);
		if (!resource || !group) {
			return; // we are not in a good state to load any state for a resource
		}

		const cache = this.doLoad();

		const mementoForResource = cache.get(resource.toString());
		if (mementoForResource) {
			return mementoForResource[group.id];
		}

		return;
	}