Fix places that trigger no-unused-lambda-capture

webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc

Index: webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc
diff --git a/webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc b/webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc
index 43cc901f006aa3aa1999a3c894898b06b34da736..09347e832447f9044c39d6ad854c9d59d157f992 100644
--- a/webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc
+++ b/webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc
@@ -507,7 +507,7 @@ void AdaptiveFirFilter::Constrain() {
   std::array<float, kFftLength> h;
   fft_.Ifft(H_[partition_to_constrain_], &h);
 
-  constexpr float kScale = 1.0f / kFftLengthBy2;
+  const float kScale = 1.0f / kFftLengthBy2;

[nisse-webrtc, 2017/08/23 09:42:02]

Could add a comment here too, on why constexpr doesn't work.

[eladalon, 2017/08/23 11:42:53]

IMHO, it would be overkill to fill the code with too many comments about this.
If someone ever tries to "fix" this, the trybots would prevent that. Or, if it
ever starts passing, and someone fixes it then - great.

   std::for_each(h.begin(), h.begin() + kFftLengthBy2,
                 [kScale](float& a) { a *= kScale; });

[kwiberg-webrtc, 2017/08/23 11:35:59]

Does it work if you change the capture list to [&] instead? That's allowed since
the lambda doesn't outlive the scope in which it is created.

[eladalon, 2017/08/23 11:42:53]

You can't capture a constexpr by reference, can you?

[kwiberg-webrtc, 2017/08/23 11:56:40]

Yes, you can. Unlike preprocessor constants and enum values, they are lvalues,
so you can take their address etc.

[eladalon, 2017/08/23 12:17:30]

Surprising, but OK. Nevertheless, I am not sure that would be an improvement of
the code. I think it would be better with const than with an unlimited capture.
Unless you feel strongly about this, I'd rather not make that change.

   std::fill(h.begin() + kFftLengthBy2, h.end(), 0.f);