We were using ToObject in a lot of places where the common case is that
we already have an object. By changing to TO_OBJECT_INLINE we don't
have to go through 5 different if statements before falling through.

We were also calling ToObject too many times in DefineObjectProperty
where we already know that obj is an object.

BUG=None
LOG=N

Review URL: https://codereview.chromium.org/1019413002

Cr-Commit-Position: refs/heads/master@{#27355}