media: Create separate target for MojoSharedBufferVideoFrame.

This is prepatory work for switching to StructTraits for VideoFrame,
which will add a dependency from //media/mojo/interfaces to
//media/mojo/common:mojo_shared_buffer_video_frame.

BUG=611224

Review-Url: https://codereview.chromium.org/2919163003
Cr-Commit-Position: refs/heads/master@{#476882}
4 files changed