Enable cpplint for more webrtc subfolders and fix all uncovered cpplint errors.

webrtc/tools/agc/activity_metric.cc

Index: webrtc/tools/agc/activity_metric.cc
diff --git a/webrtc/tools/agc/activity_metric.cc b/webrtc/tools/agc/activity_metric.cc
index 3f8235e64174f83498ca54d37e6abef5a4226b14..55280fb0d5c7976d53b7b46001ea07ed3d21b966 100644
--- a/webrtc/tools/agc/activity_metric.cc
+++ b/webrtc/tools/agc/activity_metric.cc
@@ -65,7 +65,7 @@ static void DitherSilence(AudioFrame* frame) {
     sum_squared += frame->data_[n] * frame->data_[n];
   if (sum_squared <= sum_squared_silence) {
     for (size_t n = 0; n < frame->samples_per_channel_; n++)
-      frame->data_[n] = (rand() & 0xF) - 8;
+      frame->data_[n] = (rand() & 0xF) - 8;  // NOLINT: ignore non-threadsafe.
   }
 }