Remove dangling PlayingState pointers in WebRtcAudioRenderer.

This solution is a bit of a hack, but it works. Did manual testing and ran
unit tests. Bug 697256 does not reproduce with this patch.

R=tommi@chromium.org

BUG=697256

Review-Url: https://codereview.chromium.org/2758453004
Cr-Commit-Position: refs/heads/master@{#458025}
2 files changed