[M103] Fix crash by adding nullptr check for WebContents

(cherry picked from commit 5a37dae)

Bug: 1320536
Change-Id: I1fc502e1d1872c9cdcdc2bfb5917cdf891d1050e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3647248
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Asami Doi <asamidoi@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Auto-Submit: Asami Doi <asamidoi@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1003003}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3676660
Cr-Commit-Position: refs/branch-heads/5060@{#626}
Cr-Branched-From: b83393d-refs/heads/main@{#1002911}

chrome/browser/ui/omnibox/chrome_omnibox_client.cc

@@ -385,12 +385,14 @@ void ChromeOmniboxClient::OnURLOpenedFromOmnibox(OmniboxLog* log) {
   // values (kHitFinished, kUnused, kCancelled) are recorded in
   // PrerenderManager.
   content::WebContents* web_contents = controller_->GetWebContents();
-  auto* prerender_manager = PrerenderManager::FromWebContents(web_contents);
-  if (!prerender_manager ||
-      !prerender_manager->HasSearchResultPagePrerendered()) {
-    base::UmaHistogramEnumeration(
-        internal::kHistogramPrerenderPredictionStatusDefaultSearchEngine,
-        PrerenderPredictionStatus::kNotStarted);
+  if (web_contents) {
+    auto* prerender_manager = PrerenderManager::FromWebContents(web_contents);
+    if (!prerender_manager ||
+        !prerender_manager->HasSearchResultPagePrerendered()) {
+      base::UmaHistogramEnumeration(
+          internal::kHistogramPrerenderPredictionStatusDefaultSearchEngine,
+          PrerenderPredictionStatus::kNotStarted);
+    }
   }
 
   predictors::AutocompleteActionPredictorFactory::GetForProfile(profile_)