Revert of Refactor download image-MIME-type-detection code.

chrome/browser/download/notification/download_item_notification.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/download/notification/download_item_notification.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/files/file_util.h"
@@ skipping 452 matching lines @@
   if (item_->IsDone() && image_decode_status_ == NOT_STARTED) {
     // TODO(yoshiki): Add an UMA to collect statistics of image file sizes.
 
     if (item_->GetReceivedBytes() > kMaxImagePreviewSize)
       return;
 
     DCHECK(notification_->image().IsEmpty());
 
     image_decode_status_ = IN_PROGRESS;
 
-    if (model.HasSupportedImageMimeType()) {
+    bool maybe_image = false;
+    if (mime_util::IsSupportedImageMimeType(item_->GetMimeType())) {
+      maybe_image = true;
+    } else {
+      std::string mime;
+      base::FilePath::StringType extension_with_dot =
+          item_->GetTargetFilePath().FinalExtension();
+      if (!extension_with_dot.empty() &&
+          net::GetWellKnownMimeTypeFromExtension(extension_with_dot.substr(1),
+                                                 &mime) &&
+          mime_util::IsSupportedImageMimeType(mime)) {
+        maybe_image = true;
+      }
+    }
+
+    if (maybe_image) {
       base::FilePath file_path = item_->GetFullPath();
       base::PostTaskAndReplyWithResult(
           content::BrowserThread::GetBlockingPool(), FROM_HERE,
           base::Bind(&ReadNotificationImage, file_path),
           base::Bind(&DownloadItemNotification::OnImageLoaded,
                      weak_factory_.GetWeakPtr()));
     }
   }
 }
 
@@ skipping 435 matching lines @@
   const std::string notification_id_in_message_center = notification->id();
 
   message_center::NotificationList::Notifications visible_notifications =
       message_center_->GetVisibleNotifications();
   for (const auto& notification : visible_notifications) {
     if (notification->id() == notification_id_in_message_center)
       return true;
   }
   return false;
 }