Break out code from bloated files in the BWE simulator.

No changes to functionality.

BUG=4173
R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/34209004

Cr-Original-Commit-Position: refs/heads/master@{#8374}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 14b0279416c4916534c1e76939b0b8927a208a04
15 files changed