sink_filter_ds.cc: add lock to Receive procedure to Pause().
sink_filter_ds.cc: add lock to Receive procedure to Pause().

BUG=2233
TEST=AUTO Test
R=wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/10969004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 790385fee4cbc3f2c46bcbe5e5851e75d931153c

sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc