Changed the delay estimator to be built using C++

BUG=webrtc:5724
NOPRESUBMIT=true

Review URL: https://codereview.webrtc.org/1878613002

Cr-Commit-Position: refs/heads/master@{#12336}
diff --git a/webrtc/modules/audio_processing/audio_processing.gypi b/webrtc/modules/audio_processing/audio_processing.gypi
index 2b47f7e..45b3aa3 100644
--- a/webrtc/modules/audio_processing/audio_processing.gypi
+++ b/webrtc/modules/audio_processing/audio_processing.gypi
@@ -120,10 +120,10 @@
         'typing_detection.h',
         'utility/block_mean_calculator.cc',
         'utility/block_mean_calculator.h',
-        'utility/delay_estimator.c',
+        'utility/delay_estimator.cc',
         'utility/delay_estimator.h',
         'utility/delay_estimator_internal.h',
-        'utility/delay_estimator_wrapper.c',
+        'utility/delay_estimator_wrapper.cc',
         'utility/delay_estimator_wrapper.h',
         'vad/common.h',
         'vad/gmm.cc',