Fix crash on app list start page contents not existing.

chrome/browser/ui/app_list/start_page_service.cc

Index: chrome/browser/ui/app_list/start_page_service.cc
diff --git a/chrome/browser/ui/app_list/start_page_service.cc b/chrome/browser/ui/app_list/start_page_service.cc
index d389dc2be042439244ea943d757500720c3deb4e..fa697573a7b6e0432712db261efcb472b4ff3dec 100644
--- a/chrome/browser/ui/app_list/start_page_service.cc
+++ b/chrome/browser/ui/app_list/start_page_service.cc
@@ -655,10 +655,12 @@ void StartPageService::OnURLFetchComplete(const net::URLFetcher* source) {
       }
     }
 
-    contents_->GetWebUI()->CallJavascriptFunction(
-        "appList.startPage.onAppListDoodleUpdated", *doodle_json,
-        base::StringValue(
-            UIThreadSearchTermsData(profile_).GoogleBaseURLValue()));
+    if (contents_ && contents_->GetWebUI()) {
+      contents_->GetWebUI()->CallJavascriptFunction(
+          "appList.startPage.onAppListDoodleUpdated", *doodle_json,
+          base::StringValue(
+              UIThreadSearchTermsData(profile_).GoogleBaseURLValue()));
+    }
   }
 
   // Check for a new doodle.