Zero-initialize all members of EncodedFrame.
Zero-initialize all members of EncodedFrame.

ntp_time_ms_ was missing in the default constructor, these things are
very easy to miss, so adding C++11-style initialization instead. This
also reduces init-list duplication.

BUG=
R=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44609004

git-svn-id: 03ae4fbe531b1eefc9d815f31e49022782c42458@8669 4adac7df-926f-26a2-2b94-8c16560cd09d

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