src/vs/workbench/services/textfile/common/textFileEditorModel.ts/TextFileEditorModel/updateSavedVersionId
class TextFileEditorModel:	private updateSavedVersionId(): void {
		// we remember the models alternate version id to remember when the version
		// of the model matches with the saved version on disk. we need to keep this
		// in order to find out if the model changed back to a saved version (e.g.
		// when undoing long enough to reach to a version that is saved and then to
		// clear the dirty flag)
		if (this.isResolved()) {
			this.bufferSavedVersionId = this.textEditorModel.getAlternativeVersionId();
		}
	}