Disable back/forward cache when site isolation is on

https://bugs.webkit.org/show_bug.cgi?id=265979
rdar://119287804

Reviewed by Chris Dumez.

This will make site isolation more useable while we continue to develop it.

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

Canonical link: https://commits.webkit.org/271659@main

Source/WebCore/history/BackForwardCache.cpp

@@ -210,7 +210,7 @@ static bool canCachePage(Page& page)
         return false;
     bool isCacheable = canCacheFrame(*localMainFrame, diagnosticLoggingClient, indentLevel + 1);
 
-    if (!page.settings().usesBackForwardCache() || page.isResourceCachingDisabledByWebInspector()) {
+    if (!page.settings().usesBackForwardCache() || page.isResourceCachingDisabledByWebInspector() || page.settings().siteIsolationEnabled()) {
         PCLOG("   -Page settings says b/f cache disabled");
         logBackForwardCacheFailureDiagnosticMessage(diagnosticLoggingClient, DiagnosticLoggingKeys::isDisabledKey());
         isCacheable = false;

Source/WebKit/UIProcess/WebPageProxy.cpp

@@ -1169,7 +1169,9 @@ WebBackForwardCache& WebPageProxy::backForwardCache() const
 
 bool WebPageProxy::shouldUseBackForwardCache() const
 {
-    return m_preferences->usesBackForwardCache() && backForwardCache().capacity() > 0;
+    return m_preferences->usesBackForwardCache()
+        && backForwardCache().capacity() > 0
+        && !m_preferences->siteIsolationEnabled();
 }
 
 void WebPageProxy::swapToProvisionalPage(std::unique_ptr<ProvisionalPageProxy> provisionalPage)

Tools/TestWebKitAPI/Tests/WebKitCocoa/SiteIsolation.mm

@@ -1414,8 +1414,8 @@ HTTPServer server({
     [navigationDelegate waitForDidFinishNavigation];
     checkFrameTreesInProcesses(webView.get(), { { "https://apple.com"_s } });
 
-    Util::runFor(100_ms);
-    EXPECT_TRUE(processStillRunning(iframePID));
+    while (processStillRunning(iframePID))
+        Util::spinRunLoop();
 }
 
 TEST(SiteIsolation, OpenerProcessSharing)