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It's hard to mechanically replace specializations of OwnedPtrDeleter<T>
to std::unique_ptr equivalents, so they are converted manually.

A new typedef WebMessagePortChannelUniquePtr is introduced so people can
always use std::unique_ptr with a correct deleter.

BUG=617504

Review-Url: https://codereview.chromium.org/2043583002
Cr-Commit-Position: refs/heads/master@{#398213}