Megamorphic keyed loads often load fast properties from the receiver
(as opposed to its prototype chain). They should avoid polluting the
stub cache for this.

Drive-by fix: --trace-ic printed two identical log lines for
KeyedLoadIC misses taking the LoadIC::Load path.

Review-Url: https://codereview.chromium.org/2358373002
Cr-Commit-Position: refs/heads/master@{#39684}