CL https://chromium-review.googlesource.com/499813 adds webrtc-audio-processing package. Which can be built and integrate with CRAS back in June.
I tried to continue the work this week and found emerge fail with below error when executing 'emerge-squawks webrtc-audio-processing'

libtool: link: x86_64-cros-linux-gnu-clang++  -fPIC -DPIC -shared
-nostdlib /build/cave/usr/lib/../lib64/crti.o
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/crtbeginS.o
aec/.libs/libwebrtc_audio_processing_la-aec_core.o
aec/.libs/libwebrtc_audio_processing_la-aec_rdft.o
aec/.libs/libwebrtc_audio_processing_la-aec_resampler.o
aec/.libs/libwebrtc_audio_processing_la-echo_cancellation.o
aecm/.libs/libwebrtc_audio_processing_la-echo_control_mobile.o
aecm/.libs/libwebrtc_audio_processing_la-aecm_core.o
aecm/.libs/libwebrtc_audio_processing_la-aecm_core_c.o
agc/legacy/.libs/libwebrtc_audio_processing_la-analog_agc.o
agc/legacy/.libs/libwebrtc_audio_processing_la-digital_agc.o
agc/.libs/libwebrtc_audio_processing_la-agc.o
agc/.libs/libwebrtc_audio_processing_la-agc_manager_direct.o
agc/.libs/libwebrtc_audio_processing_la-histogram.o
agc/.libs/libwebrtc_audio_processing_la-utility.o
beamformer/.libs/libwebrtc_audio_processing_la-array_util.o
beamformer/.libs/libwebrtc_audio_processing_la-covariance_matrix_generator.o
beamformer/.libs/libwebrtc_audio_processing_la-nonlinear_beamformer.o
intelligibility/.libs/libwebrtc_audio_processing_la-intelligibility_enhancer.o
intelligibility/.libs/libwebrtc_audio_processing_la-intelligibility_utils.o
logging/.libs/libwebrtc_audio_processing_la-aec_logging_file_handling.o
transient/.libs/libwebrtc_audio_processing_la-click_annotate.o
transient/.libs/libwebrtc_audio_processing_la-file_utils.o
transient/.libs/libwebrtc_audio_processing_la-moving_moments.o
transient/.libs/libwebrtc_audio_processing_la-transient_detector.o
transient/.libs/libwebrtc_audio_processing_la-transient_suppressor.o
transient/.libs/libwebrtc_audio_processing_la-wpd_node.o
transient/.libs/libwebrtc_audio_processing_la-wpd_tree.o
utility/.libs/libwebrtc_audio_processing_la-delay_estimator.o
utility/.libs/libwebrtc_audio_processing_la-delay_estimator_wrapper.o
vad/.libs/libwebrtc_audio_processing_la-gmm.o
vad/.libs/libwebrtc_audio_processing_la-pitch_based_vad.o
vad/.libs/libwebrtc_audio_processing_la-pitch_internal.o
vad/.libs/libwebrtc_audio_processing_la-pole_zero_filter.o
vad/.libs/libwebrtc_audio_processing_la-standalone_vad.o
vad/.libs/libwebrtc_audio_processing_la-vad_audio_proc.o
vad/.libs/libwebrtc_audio_processing_la-vad_circular_buffer.o
vad/.libs/libwebrtc_audio_processing_la-voice_activity_detector.o
.libs/libwebrtc_audio_processing_la-audio_buffer.o
.libs/libwebrtc_audio_processing_la-audio_processing_impl.o
.libs/libwebrtc_audio_processing_la-echo_cancellation_impl.o
.libs/libwebrtc_audio_processing_la-echo_control_mobile_impl.o
.libs/libwebrtc_audio_processing_la-gain_control_impl.o
.libs/libwebrtc_audio_processing_la-high_pass_filter_impl.o
.libs/libwebrtc_audio_processing_la-level_estimator_impl.o
.libs/libwebrtc_audio_processing_la-noise_suppression_impl.o
.libs/libwebrtc_audio_processing_la-rms_level.o
.libs/libwebrtc_audio_processing_la-splitting_filter.o
.libs/libwebrtc_audio_processing_la-processing_component.o
.libs/libwebrtc_audio_processing_la-three_band_filter_bank.o
.libs/libwebrtc_audio_processing_la-typing_detection.o
.libs/libwebrtc_audio_processing_la-voice_detection_impl.o
ns/.libs/libwebrtc_audio_processing_la-noise_suppression.o
ns/.libs/libwebrtc_audio_processing_la-ns_core.o  -Wl,--whole-archive
../../../webrtc/.libs/libwebrtc.a ../../../webrtc/base/.libs/libbase.a
../../../webrtc/system_wrappers/.libs/libsystem_wrappers.a
../../../webrtc/common_audio/.libs/libcommon_audio.a
../../../webrtc/modules/audio_coding/.libs/libaudio_coding.a
./.libs/libwebrtc_audio_processing_privatearch.a
-Wl,--no-whole-archive  -lpthread
-L/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x
-L/build/cave/lib/../lib64 -L/build/cave/usr/lib/../lib64
-L/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/../../../../x86_64-pc-linux-gnu/lib
-L/build/cave/lib -L/build/cave/usr/lib
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.x/libstdc++.so -lm -lc -lgcc_eh
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/crtendS.o
/build/cave/usr/lib/../lib64/crtn.o  -O2 -O2 -O2 -march=corei7 -g
-Wl,--no-undefined -Wl,-O1 -Wl,-O2 -Wl,--as-needed   -Wl,-soname
-Wl,libwebrtc_audio_processing.so.1 -o
.libs/libwebrtc_audio_processing.so.1.0.0
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4/complex:1174:
error: undefined reference to '__mulsc3'
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4/complex:1185:
error: undefined reference to '__divsc3'
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4/complex:1174:
error: undefined reference to '__mulsc3'
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4/complex:1185:
error: undefined reference to '__divsc3'
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4/complex:1174:
error: undefined reference to '__mulsc3'
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4/complex:1174:
error: undefined reference to '__mulsc3'
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/4.9.x/include/g++-v4/complex:1185:
error: undefined reference to '__divsc3'