CHECK if committing a failed navigation for a cancelled navigation.

This is already checked on the browser side and should never be sent to
the renderer.

Bug: 1117282
Change-Id: Ic3a5f1501a8961e5b07c6a975979bae7ec9345f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2389232Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803917}

content/renderer/render_frame_impl.cc

@@ -6378,10 +6378,11 @@ void RenderFrameImpl::SendUpdateState() {
 bool RenderFrameImpl::ShouldDisplayErrorPageForFailedLoad(
     int error_code,
     const GURL& unreachable_url) {
-  // Don't display an error page if this is simply a cancelled load.  Aside
-  // from being dumb, Blink doesn't expect it and it will cause a crash.
+  // This is already checked in `NavigationRequest::OnRequestFailedInternal` and
+  // `NavigationRequest::OnFailureChecksCompleted` on the browser side, so the
+  // renderer should never see this.
   if (error_code == net::ERR_ABORTED)
-    return false;
+    CHECK(false);
 
   // Don't display "client blocked" error page if browser has asked us not to.
   if (net::IsRequestBlockedError(error_code) &&