[Site Isolation] Session restore in a new WKWebView breaks when resto…

…ring from an existing WKWebView

https://bugs.webkit.org/show_bug.cgi?id=288162
rdar://145257058

Reviewed by Alex Christensen.

There's logic in WebPageProxy::goToBackForwardItem to send FrameState to the right frame process, but we
didn’t check if the frame actually belonged to the current page. So, after restoring session state from
another WKWebView, we could end up trying to send FrameState to a process belonging to a different page.
We should make sure the frame belongs to the current page before sending IPC to its process.

* Source/WebKit/UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::goToBackForwardItem):
* Tools/TestWebKitAPI/Tests/WebKitCocoa/SiteIsolation.mm:
(TestWebKitAPI::TEST(SiteIsolation, RestoreSessionFromAnotherWebView)):

Canonical link: https://commits.webkit.org/290832@main

Source/WebKit/UIProcess/WebPageProxy.cpp

@@ -2582,7 +2582,7 @@ RefPtr<API::Navigation> WebPageProxy::goToBackForwardItem(WebBackForwardListFram
 
     Ref frameState = item->mainFrameState();
     if (protectedPreferences()->siteIsolationEnabled()) {
-        if (RefPtr frame = WebFrameProxy::webFrame(frameItem.frameID())) {
+        if (RefPtr frame = WebFrameProxy::webFrame(frameItem.frameID()); frame && frame->page() == this) {
             process = frame->process();
             frameState = frameItem.copyFrameStateWithChildren();
         }

Tools/TestWebKitAPI/Tests/WebKitCocoa/SiteIsolation.mm

@@ -3061,6 +3061,21 @@ HTTPServer server({
     EXPECT_TRUE([webView canGoBack]);
 }
 
+TEST(SiteIsolation, RestoreSessionFromAnotherWebView)
+{
+    HTTPServer server({
+        { "/example"_s, { "<iframe src='https://webkit.org/frame'></iframe>"_s } },
+        { "/frame"_s, { "<script> alert('done'); </script>"_s } }
+    }, HTTPServer::Protocol::HttpsProxy);
+    auto [webView1, navigationDelegate] = siteIsolatedViewAndDelegate(server);
+    [webView1 loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://example.com/example"]]];
+    EXPECT_WK_STREQ([webView1 _test_waitForAlert], "done");
+
+    auto [webView2, navigationDelegate2] = siteIsolatedViewAndDelegate(server);
+    [webView2 _restoreSessionState:[webView1 _sessionState] andNavigate:YES];
+    EXPECT_WK_STREQ([webView2 _test_waitForAlert], "done");
+}
+
 static void testNavigateIframeBackForward(NSString *navigationURL, bool restoreSessionState)
 {
     HTTPServer server({