Avoid a crash when current version info is not obtainable.

chrome/browser/upgrade_detector.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/upgrade_detector.h"
 
 #include "base/command_line.h"
 #include "base/file_version_info.h"
 #include "base/scoped_ptr.h"
 #include "base/time.h"
@@ skipping 84 matching lines @@
     scoped_ptr<Version> installed_version(
         Version::GetVersionFromString(ASCIIToUTF16(reply)));
 #endif
 
     // Get the version of the currently *running* instance of Chrome.
     scoped_ptr<FileVersionInfo> version(chrome_app::GetChromeVersionInfo());
     if (version.get() == NULL) {
       NOTREACHED() << "Failed to get current file version";
       return;
     }
-    scoped_ptr<Version> running_version(Version::GetVersionFromString(
-        WideToUTF16(version->file_version())));
 
-    if (installed_version->IsHigherThan(running_version.get())) {
+    scoped_ptr<Version> running_version(
+        Version::GetVersionFromString(WideToUTF16(version->file_version())));
+    if (running_version.get() == NULL) {
+      NOTREACHED() << "Failed to parse version info";
+      return;
+    }
+
+    // |installed_version| may be NULL when the user downgrades on Linux (by
+    // switching from dev to beta channel, for example). The user needs a
+    // restart in this case as well. See http://crbug.com/46547
+    if (!installed_version.get() ||
+        installed_version->IsHigherThan(running_version.get())) {
       ChromeThread::PostTask(ChromeThread::UI, FROM_HERE,
                              upgrade_detected_task_);
       upgrade_detected_task_ = NULL;
     }
 #else  // !(defined(OS_WIN) || defined(OS_LINUX))
     DCHECK(kNotifyUserAfterMs >= 0);  // Avoid error: var defined but not used.
     NOTIMPLEMENTED();
 #endif
   }
 
@@ skipping 49 matching lines @@
 }
 
 void UpgradeDetector::NotifyOnUpgrade() {
   notify_upgrade_ = true;
 
   NotificationService::current()->Notify(
       NotificationType::UPGRADE_RECOMMENDED,
       Source<UpgradeDetector>(this),
       NotificationService::NoDetails());
 }