[stubs] Store typeof string on Oddballs.

[stubs] Store typeof string on Oddballs.

First step to simplify the TypeofStub. This is similar to the
optimization that we use for ToNumber and ToString on Oddballs already.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/1272763005

Cr-Commit-Position: refs/heads/master@{#30108}