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

chrome/browser/download/notification/download_item_notification.cc

Index: chrome/browser/download/notification/download_item_notification.cc
diff --git a/chrome/browser/download/notification/download_item_notification.cc b/chrome/browser/download/notification/download_item_notification.cc
index e98e7d0ae4a095328ff0bca37e2a15f1455534a0..cc5f995e554d201ef2db69a8658e33d220a33ff9 100644
--- a/chrome/browser/download/notification/download_item_notification.cc
+++ b/chrome/browser/download/notification/download_item_notification.cc
@@ -470,7 +470,22 @@
 
     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,