Move download filename determintion into a separate class.

chrome/browser/download/download_crx_util.cc

Index: chrome/browser/download/download_crx_util.cc
diff --git a/chrome/browser/download/download_crx_util.cc b/chrome/browser/download/download_crx_util.cc
index 3834b40bd6e3f6f15e6de6c1fda515cb02ee0053..d3afa8b188ca7c8cc8feb9a2e309fa8bcf336af1 100644
--- a/chrome/browser/download/download_crx_util.cc
+++ b/chrome/browser/download/download_crx_util.cc
@@ -125,8 +125,12 @@ bool IsExtensionDownload(const DownloadItem& download_item) {
 }
 
 bool OffStoreInstallAllowedByPrefs(Profile* profile, const DownloadItem& item) {
-  extensions::ExtensionPrefs* prefs = extensions::ExtensionSystem::Get(
-      profile)->extension_service()->extension_prefs();
+  ExtensionService* service = extensions::ExtensionSystem::Get(
+      profile)->extension_service();
+  if (!service)
+    return false;
+
+  extensions::ExtensionPrefs* prefs = service->extension_prefs();
   CHECK(prefs);
 
   extensions::URLPatternSet url_patterns = prefs->GetAllowedInstallSites();