Use DCHECKs when observing only a single notification.

chrome/browser/media/permission_bubble_media_access_handler.cc

 // Copyright 2015 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/media/permission_bubble_media_access_handler.h"
 
 #include <utility>
 
 #include "base/metrics/field_trial.h"
 #include "chrome/browser/media/media_permission.h"
@@ skipping 220 matching lines @@
   }
 
   callback.Run(devices, result, std::move(ui));
 }
 
 void PermissionBubbleMediaAccessHandler::Observe(
     int type,
     const content::NotificationSource& source,
     const content::NotificationDetails& details) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  if (type == content::NOTIFICATION_WEB_CONTENTS_DESTROYED) {
-    content::WebContents* web_contents =
-        content::Source<content::WebContents>(source).ptr();
-    pending_requests_.erase(web_contents);
-  }
+  DCHECK_EQ(content::NOTIFICATION_WEB_CONTENTS_DESTROYED, type);
+
+  pending_requests_.erase(content::Source<content::WebContents>(source).ptr());
 }