MSE: Test no muxed discontinuity forced by audio frame partial front trimming

MSE: Test no muxed discontinuity forced by audio frame partial front trimming

This change adds frame processor tests to cover the behavior recently
landed from bad1c509 that changed "segments" appendMode's partial front
trimming logic.

BUG=408216
R=dalecurtis@chromium.org
TEST=new segments test fails before and passes after bad1c509, new sequence test passes before and after

Committed: https://crrev.com/772b33525c1dfbe3c1fd0ea06fd1944a40ad7ffb
Cr-Commit-Position: refs/heads/master@{#294920}

[wolenetz, 2014-09-15 21:21:53]

PTAL

[DaleCurtis, 2014-09-15 21:37:13]

lgtm

[wolenetz, 2014-09-15 21:37:58]

The CQ bit was checked by wolenetz@chromium.org

[commit-bot: I haz the power, 2014-09-15 22:04:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/567403004/1

[commit-bot: I haz the power, 2014-09-15 23:31:46]

Committed patchset #1 (id:1) as bf05bb8682cc7f040700fa6c1746f332af65a31b

[commit-bot: I haz the power, 2014-09-15 23:34:24]

Patchset 1 (id:??) landed as
https://crrev.com/772b33525c1dfbe3c1fd0ea06fd1944a40ad7ffb
Cr-Commit-Position: refs/heads/master@{#294920}