Avoid a crash when current version info is not obtainable.

chrome/browser/upgrade_detector.cc

Index: chrome/browser/upgrade_detector.cc
diff --git a/chrome/browser/upgrade_detector.cc b/chrome/browser/upgrade_detector.cc
index ae92c99692bdc8a42e968921eb47d5815086aaf9..49db0ce83e1b7a0668fc20826d3d92e8ad191e58 100644
--- a/chrome/browser/upgrade_detector.cc
+++ b/chrome/browser/upgrade_detector.cc
@@ -102,10 +102,19 @@ class DetectUpgradeTask : public Task {
       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;