See https://build.chromium.org/p/chromium.fyi/builders/Site%20Isolation%20Linux/builds/22758, where the failures started.

The following tests are failing:

* http/tests/local/fileapi/send-dragged-file-form-iso-2022-jp.html
* http/tests/local/fileapi/send-dragged-file-form-utf-8.html
* http/tests/local/fileapi/send-dragged-file-form-windows-1252.html
* http/tests/local/fileapi/send-dragged-file-form-x-user-defined.html
* http/tests/local/fileapi/send-dragged-file-form.html
* virtual/mojo-loading/http/tests/local/fileapi/send-dragged-file-form-iso-2022-jp.html
* virtual/mojo-loading/http/tests/local/fileapi/send-dragged-file-form-utf-8.html
* virtual/mojo-loading/http/tests/local/fileapi/send-dragged-file-form-windows-1252.html
* virtual/mojo-loading/http/tests/local/fileapi/send-dragged-file-form-x-user-defined.html
* virtual/mojo-loading/http/tests/local/fileapi/send-dragged-file-form.html

They were all added in https://chromium-review.googlesource.com/c/chromium/src/+/755342

Sample failure output for a couple of tests:

http/tests/local/fileapi/send-dragged-file-form.html:
This is a testharness.js-based test.
FAIL Upload file-for-drag-to-send3.txt (ASCII) in UTF-8 form promise_test: Unhandled rejection with value: object "TypeError: Cannot read property 'body' of null"
Harness: the test ran to completion.

http/tests/local/fileapi/send-dragged-file-form-x-user-defined.html:
This is a testharness.js-based test.
FAIL Upload file-for-drag-to-send3.txt (ASCII) in x-user-defined form promise_test: Unhandled rejection with value: object "TypeError: Cannot read property 'body' of null"
FAIL Upload file-for-drag-to-send3-ïŸ°ïž“ïžƒïž .txt (x-user-defined) in x-user-defined form promise_test: Unhandled rejection with value: object "TypeError: Cannot read property 'body' of null"
FAIL Upload file-for-drag-to-send3-☺😂.txt (windows-1252) in x-user-defined form promise_test: Unhandled rejection with value: object "TypeError: Cannot read property 'body' of null"
FAIL Upload file-for-drag-to-send3-★星★.txt (JIS X 0201 and JIS X 0208) in x-user-defined form promise_test: Unhandled rejection with value: object "TypeError: Cannot read property 'body' of null"
FAIL Upload file-for-drag-to-send3-☺😂.txt (Unicode) in x-user-defined form promise_test: Unhandled rejection with value: object "TypeError: Cannot read property 'body' of null"
FAIL Upload file-for-drag-to-send3-ABC~‾¥≈¤･・•∙·☼★星🌟星★☼·∙•・･¤≈¥‾~XYZ.txt (Unicode) in x-user-defined form promise_test: Unhandled rejection with value: object "TypeError: Cannot read property 'body' of null"
Harness: the test ran to completion.

bsittler@: can you please take a look?  You can repro locally by passing --additional-drt-flag=--site-per-process to run-webkit-tests.  If your new tests have cross-origin iframes, they would become out-of-process iframes with --site-per-process, and there might be an issue with that and drag-and-drop (or this could be a test issue).  +paulmeyer@, who worked on drag-and-drop support for OOPIFs, just in case.

I'll go ahead and disable these tests on our bots in the meantime.