Disable flaky DownloadExtensionTest[...]EmptyBasenameInvalid

Full test name:
DownloadExtensionTest.DownloadExtensionTest_OnDeterminingFilename_EmptyBasenameInvalid

TBR=qinmin@chromium.org

Bug: 1147804
Change-Id: I42d8fd39e2d2181045c7343c872c9d2f4665f729
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532573Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826240}

chrome/browser/extensions/api/downloads/downloads_api_browsertest.cc

@@ -3524,9 +3524,10 @@ IN_PROC_BROWSER_TEST_F(
                           result_id)));
 }
 
+// Flaky. crbug.com/1147804
 IN_PROC_BROWSER_TEST_F(
     DownloadExtensionTest,
-    DownloadExtensionTest_OnDeterminingFilename_EmptyBasenameInvalid) {
+    DISABLED_DownloadExtensionTest_OnDeterminingFilename_EmptyBasenameInvalid) {
   GoOnTheRecord();
   LoadExtension("downloads_split");
   AddFilenameDeterminer();