The blink layout test:
https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/http/tests/inspector/network/network-datasaver-warning.html
doesn't work with PlzNavigate(--enable-browser-side-navigation)

The test checks that a console log warning is displayed on reload when the
Data-Saver is enabled.

The reason the test fails is that ContentBrowserClient::IsDataSaverEnabled() is
implemented only by ChromeContentBrowserClient. The blink layout tests are
using ShellContentBrowserClient instead. So from the browser point of view
Data-Saver is always disabled in layout tests.

The solution would be to replace this layout test with a chrome browser test.

+CC: FYI