chrome: Update expectations with same-site BFCache enabled (fixes issue #3301)

With same-site BFCache enabled every navigation can now potentially be served
via the BFCache. To support this internally a new top-level RenderFrame object
may be created for each new navigation. As a result, OnBrowserCreated may now
be called multiple times with the same browser ID in a given renderer process
(a behavior previously only seen with cross-site navigations and different
renderer processes).

BFCache navigations do not trigger the same Chromium notifications as a normal
load. To avoid breaking CEF API usage expectations we now synthetically
generate the load-related callbacks that would otherwise be missing
(OnLoadingStateChange with isLoading=true, OnLoadStart, OnLoadEnd). The
|httpStatusCode| argument to OnLoadEnd will be 0 in this case.

To test:
- Run `FrameHandlerTest.*:MessageRouterTest.*:NavigationTest.*`
- Run `NavigationTest.LoadSameOriginLoadURL` for OnBrowserCreated behavior.
- Run `NavigationTest.History` for load-related callback behavior.

libcef/browser/browser_info.cc

@@ -168,13 +168,10 @@ void CefBrowserInfo::FrameHostStateChanged(
            content::RenderFrameHost::LifecycleState::kInBackForwardCache) &&
       new_state == content::RenderFrameHost::LifecycleState::kActive) {
     if (auto frame = GetFrameForHost(host)) {
-      // Should only occur for the main frame.
-      CHECK(frame->IsMain());
-
       // Update the associated RFH, which may have changed.
       frame->MaybeReAttach(this, host);
 
-      {
+      if (frame->IsMain()) {
         // Update the main frame object.
         NotificationStateLock lock_scope(this);
         SetMainFrame(browser_, frame);