Use DCHECKs when observing only a single notification.

chrome/browser/chromeos/first_run/drive_first_run_controller.cc

Index: chrome/browser/chromeos/first_run/drive_first_run_controller.cc
diff --git a/chrome/browser/chromeos/first_run/drive_first_run_controller.cc b/chrome/browser/chromeos/first_run/drive_first_run_controller.cc
index 1ac23aa09bfc4ddb101b6f9ba9f72991133c7e28..bd72bacfbc6078dadb3dcd181781ecffe22efd4d 100644
--- a/chrome/browser/chromeos/first_run/drive_first_run_controller.cc
+++ b/chrome/browser/chromeos/first_run/drive_first_run_controller.cc
@@ -328,13 +328,12 @@ void DriveWebContentsManager::Observe(
     int type,
     const content::NotificationSource& source,
     const content::NotificationDetails& details) {
-  if (type == chrome::NOTIFICATION_BACKGROUND_CONTENTS_OPENED) {
-    const std::string app_id = base::UTF16ToUTF8(
-        content::Details<BackgroundContentsOpenedDetails>(details)
-            ->application_id);
-    if (app_id == app_id_)
-      OnOfflineInit(true, DriveFirstRunController::OUTCOME_OFFLINE_ENABLED);
-  }
+  DCHECK_EQ(chrome::NOTIFICATION_BACKGROUND_CONTENTS_OPENED, type);
+  const std::string app_id = base::UTF16ToUTF8(
+      content::Details<BackgroundContentsOpenedDetails>(details)
+          ->application_id);
+  if (app_id == app_id_)
+    OnOfflineInit(true, DriveFirstRunController::OUTCOME_OFFLINE_ENABLED);
 }
 
 ////////////////////////////////////////////////////////////////////////////////