Added new mixer to |check_targets| in .gn and fixed include/depend errors.

webrtc/modules/audio_mixer/new_audio_conference_mixer_impl.cc

Index: webrtc/modules/audio_mixer/new_audio_conference_mixer_impl.cc
diff --git a/webrtc/modules/audio_mixer/new_audio_conference_mixer_impl.cc b/webrtc/modules/audio_mixer/new_audio_conference_mixer_impl.cc
index 5be76ec4d02df415711fc9fa9a1e504ea86da213..48380fc550129a6ea62882fe96941a5148473701 100644
--- a/webrtc/modules/audio_mixer/new_audio_conference_mixer_impl.cc
+++ b/webrtc/modules/audio_mixer/new_audio_conference_mixer_impl.cc
@@ -19,7 +19,6 @@
 #include "webrtc/modules/utility/include/audio_frame_operations.h"
 #include "webrtc/system_wrappers/include/critical_section_wrapper.h"
 #include "webrtc/system_wrappers/include/trace.h"
-#include "webrtc/voice_engine/utility.h"
 
 namespace webrtc {
 namespace {
@@ -142,6 +141,8 @@ NewAudioConferenceMixerImpl::NewAudioConferenceMixerImpl(int id)
   thread_checker_.DetachFromThread();
 }
 
+NewAudioConferenceMixerImpl::~NewAudioConferenceMixerImpl() {}
+
 bool NewAudioConferenceMixerImpl::Init() {
   crit_.reset(CriticalSectionWrapper::CreateCriticalSection());
   if (crit_.get() == NULL)