Update audio code to use size_t more correctly,

webrtc/modules/audio_coding/neteq/dtmf_tone_generator.cc

Index: webrtc/modules/audio_coding/neteq/dtmf_tone_generator.cc
diff --git a/webrtc/modules/audio_coding/neteq/dtmf_tone_generator.cc b/webrtc/modules/audio_coding/neteq/dtmf_tone_generator.cc
index 45601c04d42c2cd1191ab2f64f44ce969a5d2fb3..f4d5190c615ab2c0ecd3eddd007b6c1301522ce8 100644
--- a/webrtc/modules/audio_coding/neteq/dtmf_tone_generator.cc
+++ b/webrtc/modules/audio_coding/neteq/dtmf_tone_generator.cc
@@ -149,18 +149,18 @@ void DtmfToneGenerator::Reset() {
 }
 
 // Generate num_samples of DTMF signal and write to |output|.
-int DtmfToneGenerator::Generate(int num_samples,
+int DtmfToneGenerator::Generate(size_t num_samples,
                                 AudioMultiVector* output) {
   if (!initialized_) {
     return kNotInitialized;
   }
 
-  if (num_samples < 0 || !output) {
+  if (!output) {
     return kParameterError;
   }
 
   output->AssertSize(num_samples);
-  for (int i = 0; i < num_samples; ++i) {
+  for (size_t i = 0; i < num_samples; ++i) {
     // Use recursion formula y[n] = a * y[n - 1] - y[n - 2].
     int16_t temp_val_low = ((coeff1_ * sample_history1_[1] + 8192) >> 14)
         - sample_history1_[0];
@@ -186,7 +186,7 @@ int DtmfToneGenerator::Generate(int num_samples,
     output->CopyChannel(0, channel);
   }
 
-  return num_samples;
+  return static_cast<int>(num_samples);
 }
 
 bool DtmfToneGenerator::initialized() const {