Fix stream errors that occur after a stream starts not propagating.

Currently a stream was treated as having no errors even if an error occurs after reading starts. This change plumbs the error through.

This fixes the following tests with PlzNavigate:
ChromeURLDataManagerTest.LargeResourceScale
ChromeURLDataManagerTest.UnknownResource

BUG=426162,508957,504347

Review-Url: https://codereview.chromium.org/2368913002
Cr-Commit-Position: refs/heads/master@{#421237}