/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */
import { InjectionToken } from '@angular/core';
import * as i0 from "@angular/core";
/**
 * Injection token to configure which origins should be excluded
 * from the preconnect checks. It can either be a single string or an array of strings
 * to represent a group of origins, for example:
 *
 * ```typescript
 *  {provide: PRECONNECT_CHECK_BLOCKLIST, useValue: 'https://your-domain.com'}
 * ```
 *
 * or:
 *
 * ```typescript
 *  {provide: PRECONNECT_CHECK_BLOCKLIST,
 *   useValue: ['https://your-domain-1.com', 'https://your-domain-2.com']}
 * ```
 *
 * @publicApi
 */
export declare const PRECONNECT_CHECK_BLOCKLIST: InjectionToken<(string | string[])[]>;
/**
 * Contains the logic to detect whether an image, marked with the "priority" attribute
 * has a corresponding `<link rel="preconnect">` tag in the `document.head`.
 *
 * Note: this is a dev-mode only class, which should not appear in prod bundles,
 * thus there is no `ngDevMode` use in the code.
 */
export declare class PreconnectLinkChecker {
    private document;
    /**
     * Set of <link rel="preconnect"> tags found on this page.
     * The `null` value indicates that there was no DOM query operation performed.
     */
    private preconnectLinks;
    private alreadySeen;
    private window;
    private blocklist;
    constructor();
    private populateBlocklist;
    /**
     * Checks that a preconnect resource hint exists in the head for the
     * given src.
     *
     * @param rewrittenSrc src formatted with loader
     * @param originalNgSrc ngSrc value
     */
    assertPreconnect(rewrittenSrc: string, originalNgSrc: string): void;
    private queryPreconnectLinks;
    ngOnDestroy(): void;
    static ɵfac: i0.ɵɵFactoryDeclaration<PreconnectLinkChecker, never>;
    static ɵprov: i0.ɵɵInjectableDeclaration<PreconnectLinkChecker>;
}