This change avoids calling neteq_->EnableVad() and DisableVad from the AcmReceiver constructor. Instead, the new member enable_post_decode_vad is added to NetEq's config struct. It is disabled by defualt, but ACM sets it to enabled. This preserves the behavior both of NetEq stand-alone (i.e., in tests) and of ACM. BUG=webrtc:3520 Review URL: https://codereview.webrtc.org/1425133002 Cr-Commit-Position: refs/heads/master@{#10476}