Fix the serialization for values in std::unique_ptrs.

In the ToValueImpl specialization for std::unique_ptr<T>, call ToValue
with the dereferenced type. All specializations take const&, which would
previously result in a call to ToValue(const*&), resulting in a wrong
specialization to be selected.

BUG=546953

Review-Url: https://codereview.chromium.org/2533083003
Cr-Commit-Position: refs/heads/master@{#434955}
2 files changed