Solve TSan warning about unlocking an unlocked mutex.

In my previous cl, https://webrtc-codereview.appspot.com/52479004/, there is 'UnLock()' left when we switched to scoped lock, which will cause TSan warning sometimes.
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WARNING: ThreadSanitizer: unlock of an unlocked mutex (or by a wrong thread) (pid=9981)
#0 pthread_mutex_unlock <null> (libjingle_peerconnection_unittest+0x00000046836f)
#1 webrtc::CriticalSectionPosix::Leave() webrtc/system_wrappers/source/critical_section_posix.cc:39:10 (libjingle_peerconnection_unittest+0x000000bc368d)
#2 ~CriticalSectionScoped webrtc/system_wrappers/interface/critical_section_wrapper.h:46:48 (libjingle_peerconnection_unittest+0x000000a61fcb)
#3 webrtc::AudioDeviceLinuxPulse::RecThreadProcess() webrtc/modules/audio_device/linux/audio_device_pulse_linux.cc:3003 (libjingle_peerconnection_unittest+0x000000a61fcb)
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BUG=3056
TEST=bots
R=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/56439004

Cr-Commit-Position: refs/heads/master@{#9282}
1 file changed