chrome: Fix callbacks for different Profile types (see issue #2969)

- Only install network intercepts for Profiles that have an associated
  CefBrowserContext. For incognito windows the CefBrowserContext is
  associated with the OffTheRecordProfileImpl's original Profile.
- cefsimple: Return the default CefClient instance for browser windows
  created via the Chrome UI, and allow Chrome to show error pages.

libcef/browser/chrome/chrome_content_browser_client_cef.cc

@@ -170,6 +170,13 @@ bool ChromeContentBrowserClientCef::WillCreateURLLoaderFactory(
     return use_proxy;
   }
 
+  // Don't intercept requests for Profiles that were not created by CEF.
+  // For example, the User Manager profile created via
+  // profiles::CreateSystemProfileForUserManager.
+  auto profile = Profile::FromBrowserContext(browser_context);
+  if (!CefBrowserContext::FromBrowserContext(profile->GetOriginalProfile()))
+    return false;
+
   auto request_handler = net_service::CreateInterceptedRequestHandler(
       browser_context, frame, render_process_id,
       type == URLLoaderFactoryType::kNavigation,

libcef/browser/net_service/resource_request_handler_wrapper.cc

@@ -260,8 +260,10 @@ class InterceptedRequestHandlerWrapper : public InterceptedRequestHandler {
       CEF_REQUIRE_UIT();
 
       browser_context_ = browser_context;
+
+      auto profile = Profile::FromBrowserContext(browser_context);
       auto cef_browser_context =
-          CefBrowserContext::FromBrowserContext(browser_context);
+          CefBrowserContext::FromBrowserContext(profile->GetOriginalProfile());
       iothread_state_ = cef_browser_context->iothread_state();
       DCHECK(iothread_state_);
       cookieable_schemes_ = cef_browser_context->GetCookieableSchemes();