The KeyedStoreMode that we get out of the FeedbackNexus doesn't
necessarily need to apply when we have "static knowledge" about
the receiver, i.e. when the receiver is a known JSTypedArray, but
the KEYED_STORE_IC has seen only JSArray instances so far. The
DCHECK was too restrictive in this case, since we can just ignore
the KEYED_STORE_IC mode (like we ignore the maps).

BUG=chromium:685050
R=ishell@chromium.org

Review-Url: https://codereview.chromium.org/2668643002
Cr-Commit-Position: refs/heads/master@{#42810}