MessageQueue uses Deque<OwnPtr<> >
MessageQueue uses Deque<OwnPtr<> >

The MessageQueue class description comment contains
the following: "Essentially, MessageQueue acts as a
queue of OwnPtr<DataType>"

This patch makes the MessageQueue actually contain
the queue of OwnPtr's instead of queue of plain
pointers (as it was before) making the code simpler
and more compact.

Review URL: https://codereview.chromium.org/253753004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@172777 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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