For dictionary-mode receivers, the KeyedStoreGeneric stub can store
properties directly in most cases. Doing so avoids the need to have
an entry in the stub cache for every map/property combination.

Original review: https://codereview.chromium.org/2504403005/

Review-Url: https://codereview.chromium.org/2528883003
Cr-Commit-Position: refs/heads/master@{#41272}