http/tests/site-isolation/basic-iframe.html is flaky on iOS

https://bugs.webkit.org/show_bug.cgi?id=252504
rdar://105613555

Unreviewed test gardening.

Work has been done, tests pass.

* LayoutTests/platform/ios/TestExpectations:
* Tools/TestWebKitAPI/Tests/WebKitCocoa/SiteIsolation.mm:
(TestWebKitAPI::TEST):

Canonical link: https://commits.webkit.org/265966@main

LayoutTests/platform/ios/TestExpectations

@@ -4319,8 +4319,6 @@ webkit.org/b/251875 fast/dynamic/create-renderer-for-whitespace-only-text.html [
 
 webkit.org/b/257832 imported/w3c/web-platform-tests/html/rendering/the-details-element/summary-text-decoration.html [ ImageOnlyFailure ]
 
-webkit.org/b/252504 http/tests/site-isolation [ Skip ]
-
 http/wpt/service-workers/basic-fetch-with-contentfilter-allow-after-adding-data.html [ Pass ]
 http/wpt/service-workers/basic-fetch-with-contentfilter.https.html [ Pass ]
 

Tools/TestWebKitAPI/Tests/WebKitCocoa/SiteIsolation.mm

@@ -898,8 +898,6 @@ HTTPServer server({
     Util::run(&done);
 }
 
-// FIXME: This test times out on the iOS simulator. Investigate and fix.
-#if PLATFORM(MAC)
 TEST(SiteIsolation, MainFrameWithTwoIFramesInTheSameProcess)
 {
     HTTPServer server({
@@ -911,8 +909,7 @@ HTTPServer server({
     [navigationDelegate allowAnyTLSCertificate];
 
     auto configuration = server.httpsProxyConfiguration();
-    // FIXME: call enableSiteIsolation to make this actually use site isolation
-    // once we make changes so that this isn't flaky.
+    enableSiteIsolation(configuration);
 
     auto webView = adoptNS([[WKWebView alloc] initWithFrame:CGRectZero configuration:configuration]);
     webView.get().navigationDelegate = navigationDelegate.get();
@@ -938,16 +935,14 @@ HTTPServer server({
         EXPECT_NE(childFramePid, 0);
         EXPECT_NE(otherChildFramePid, 0);
         EXPECT_EQ(childFramePid, otherChildFramePid);
-        // FIXME: Switch to EXPECT_NE once siteIsolation is enabled.
-        EXPECT_EQ(mainFramePid, childFramePid);
+        EXPECT_NE(mainFramePid, childFramePid);
         EXPECT_WK_STREQ(mainFrame.securityOrigin.host, "example.com");
         EXPECT_WK_STREQ(childFrame.securityOrigin.host, "webkit.org");
         EXPECT_WK_STREQ(otherChildFrame.securityOrigin.host, "webkit.org");
         done = true;
     }];
     Util::run(&done);
 }
-#endif
 
 TEST(SiteIsolation, ChildBeingNavigatedToMainFrameDomainByParent)
 {