core(canonical): remove cross-origin check

lighthouse-core/audits/seo/canonical.js

@@ -38,11 +38,6 @@ const UIStrings = {
    * @example {https://example.com/} url
    */
   explanationPointsElsewhere: 'Points to another `hreflang` location ({url})',
-  /**
-   * @description Explanatory message stating that there was a failure in an audit caused by a URL pointing to a different domain.
-   * @example {https://example.com/} url
-   * */
-  explanationDifferentDomain: 'Points to a different domain ({url})',
   /** Explanatory message stating that the page's canonical URL was pointing to the domain's root URL, which is a common mistake. "points" refers to the action of the 'rel=canonical' referencing another link. "root" refers to the starting/home page of the website. "domain" refers to the registered domain name of the website. */
   explanationRoot: 'Points to the domain\'s root URL (the homepage), ' +
     'instead of an equivalent page of content',
@@ -174,15 +169,6 @@ class Canonical extends Audit {
       };
     }
 
-    // bing and yahoo don't allow canonical URLs pointing to different domains, it's also
-    // a common mistake to publish a page with canonical pointing to e.g. a test domain or localhost
-    if (!URL.rootDomainsMatch(canonicalURL, baseURL)) {
-      return {
-        score: 0,
-        explanation: str_(UIStrings.explanationDifferentDomain, {url: canonicalURL.href}),
-      };
-    }
-
     // another common mistake is to have canonical pointing from all pages of the website to its root
     if (
       canonicalURL.origin === baseURL.origin &&

lighthouse-core/test/audits/seo/canonical-test.js

@@ -127,26 +127,6 @@ describe('SEO: Document has valid canonical link', () => {
     });
   });
 
-  it('fails when canonical points to a different domain', () => {
-    const finalUrl = 'http://localhost.test';
-    const mainResource = {url: finalUrl};
-    const devtoolsLog = networkRecordsToDevtoolsLog([mainResource]);
-    const artifacts = {
-      devtoolsLogs: {[CanonicalAudit.DEFAULT_PASS]: devtoolsLog},
-      URL: {finalUrl},
-      LinkElements: [
-        link({rel: 'canonical', source: 'head', href: 'https://example.com'}),
-      ],
-    };
-
-    const context = {computedCache: new Map()};
-    return CanonicalAudit.audit(artifacts, context).then(auditResult => {
-      assert.equal(auditResult.score, 0);
-      expect(auditResult.explanation)
-        .toBeDisplayString('Points to a different domain (https://example.com/)');
-    });
-  });
-
   it('passes when canonical points to the root while current URL is also the root', async () => {
     const finalUrl = 'https://example.com/';
     const mainResource = {