Use DCHECKs when observing only a single notification.

chrome/browser/chromeos/extensions/external_cache.cc

 // Copyright (c) 2013 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/chromeos/extensions/external_cache.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 136 matching lines @@
     const PutExternalExtensionCallback& callback) {
   local_cache_.PutExtension(
       id, std::string(), crx_file_path, version,
       base::Bind(&ExternalCache::OnPutExternalExtension,
                  weak_ptr_factory_.GetWeakPtr(), id, callback));
 }
 
 void ExternalCache::Observe(int type,
                             const content::NotificationSource& source,
                             const content::NotificationDetails& details) {
-  switch (type) {
-    case extensions::NOTIFICATION_EXTENSION_INSTALL_ERROR: {
-      extensions::CrxInstaller* installer =
-          content::Source<extensions::CrxInstaller>(source).ptr();
-      OnDamagedFileDetected(installer->source_file());
-      break;
-    }
+  DCHECK_EQ(extensions::NOTIFICATION_EXTENSION_INSTALL_ERROR, type);
 
-    default:
-      NOTREACHED();
-  }
+  extensions::CrxInstaller* installer =
+      content::Source<extensions::CrxInstaller>(source).ptr();
+  OnDamagedFileDetected(installer->source_file());
 }
 
 void ExternalCache::OnExtensionDownloadFailed(
     const std::string& id,
     extensions::ExtensionDownloaderDelegate::Error error,
     const extensions::ExtensionDownloaderDelegate::PingResult& ping_result,
     const std::set<int>& request_ids) {
   if (error == NO_UPDATE_AVAILABLE) {
     if (!cached_extensions_->HasKey(id)) {
       LOG(ERROR) << "ExternalCache extension " << id
@@ skipping 186 matching lines @@
   OnPutExtension(id, file_path, file_ownership_passed);
   callback.Run(id, !file_ownership_passed);
 }
 
 std::string ExternalCache::Delegate::GetInstalledExtensionVersion(
     const std::string& id) {
   return std::string();
 }
 
 }  // namespace chromeos