Repro:
$ DISPLAY=:20 third_party/WebKit/Tools/Scripts/run-webkit-tests -t gn -v --additional-drt-flag=--site-per-process --additional-drt-flag=--no-sandbox http/tests/misc/copy-resolves-urls.html
In this test case "Copy" is performed in one renderer process, and "Paste" is performed in another renderer process (after navigating the page to a different site). This leads to trouble with --site-per-process, because the fake clipboard used during the tests is not replicated across the renderers - i.e. the call to MockWebClipboardImpl::writeHTML happens in one renderer process and the calls to MockWebClipboardImpl::readAvailableTypes, isFormatAvailable, readPlainText happen in another renderer process.
Replication is a bit tricky, because MockWebClipboardImpl is implemented in content/test, while replication across renderers (for other layout-test-related state) is happening via LayoutTestRuntimeFlags which is implemented in components/test_runner.
At any rate - this seems like a test issue, so nothing that should impact --isolate-extensions launch.
Comment 1 by dcheng@chromium.org
, Apr 29 2016