Adding nullptr check to DSE preconnect

Bug: 1036489
Change-Id: I64bea0d19217483cb040a0bc0ba2697809a96ade
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1993800Reviewed-by: Robert Ogden <robertogden@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729918}

chrome/browser/navigation_predictor/search_engine_preconnector.cc

@@ -123,6 +123,9 @@ void SearchEnginePreconnector::PreconnectDSE() {
   auto* loading_predictor = predictors::LoadingPredictorFactory::GetForProfile(
       Profile::FromBrowserContext(browser_context_));
 
+  if (!loading_predictor)
+    return;
+
   loading_predictor->preconnect_manager()->StartPreconnectUrl(
       preconnect_url, true /* allow_credentials */,
       net::NetworkIsolationKey(url::Origin::Create(preconnect_url),