[Downloads] Treat ERR_NETWORK_CHANGED as INTERRUPT_REASON_NETWORK_DISCONNECTED.

This should ideally have a better named interrupt reason, but the mapping
allows the same treatment to be extended for ERR_NETWORK_CHANGED as
ERR_INTERNET_DISCONNECTED.

R=svaldez@chromium.org
BUG=7648

Review URL: https://codereview.chromium.org/1719283002

Cr-Commit-Position: refs/heads/master@{#377421}
1 file changed