port 1a5751f9 (r29956)

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.

BUG=

Review URL: https://codereview.chromium.org/1265113002

Cr-Commit-Position: refs/heads/master@{#29963}