Port 1a5751f9

Original commit message:
    Since we need the notion of a dummy vector ic, we can use that to avoid
    a special case of the IC constructor. Also, consolidate the two dummy
    ICs into one.

R=mvstanton@chromium.org, michael_dawson@ca.ibm.com, jyan@ca.ibm.com, joransiu@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1261433007

Cr-Commit-Position: refs/heads/master@{#29959}