r419019 added blocking of requests with nested URLs with extension origins originating from non-extension processes.  Looks like these checks are incompatible with PlzNavigate and cause the following browser_tests failures:

WebViewGuestTouchFocusTest.TouchFocusesBrowserPluginInEmbedder
WebViewScrollGuestContent/WebViewScrollGuestContentTest.ScrollGuestContent/0
WebViewScrollBubbling/WebViewGuestScrollTouchTest.TestGuestGestureScrollsBubble/0
WebViewScrollBubbling/WebViewGuestScrollTouchTest.TestGuestGestureScrollsBubble/1
WebViewScrollBubbling/WebViewGuestScrollTouchTest.TestGuestGestureScrollsBubble/2
WebViewScrollBubbling/WebViewGuestScrollTouchTest.TestGuestGestureScrollsBubble/3
WebViewTests/WebViewFocusTest.TouchFocusesEmbedder/0
ProcessManagerBrowserTest.NestedURLNavigationsToExtensionAllowed

The failures started in https://build.chromium.org/p/chromium.fyi/builders/Browser%20Side%20Navigation%20Linux/builds/21327

The WebView tests are failing because the <webview> src in these tests is set to a chrome-extension:// URL (from same app as where the embedder is served from), and the <webview> load is blocked.  I don't quite know how these requests are issued with PlzNavigate, but from what Nasko tells me, they use blob URLs underneath with no renderer process being responsible for the request, and further the <webview> makes it seem like a top-level navigation, so it kind of makes sense why the blocking occurs.  We'll need to fix this to work with PlzNavigate.

I'll disable these tests while I investigate further.