Add vector_math::FMUL. Replace audio_util::AdjustVolume.

media/audio/mac/audio_auhal_mac.cc

Index: media/audio/mac/audio_auhal_mac.cc
diff --git a/media/audio/mac/audio_auhal_mac.cc b/media/audio/mac/audio_auhal_mac.cc
index 20df6f5d2ae56417000101c1302d503ca0a120ed..b2a8828fec12f6548a47a40cd24a99aa1f976a42 100644
--- a/media/audio/mac/audio_auhal_mac.cc
+++ b/media/audio/mac/audio_auhal_mac.cc
@@ -178,8 +178,6 @@ void AUHALStream::Stop() {
 
 void AUHALStream::SetVolume(double volume) {
   volume_ = static_cast<float>(volume);
-
-  // TODO(crogers): set volume property
 }
 
 void AUHALStream::GetVolume(double* volume) {
@@ -251,6 +249,7 @@ OSStatus AUHALStream::Render(
         input_bus_.get(),
         output_bus_.get(),
         AudioBuffersState(0, hardware_pending_bytes));
+    output_bus_->Scale(volume_);
   }
 
   return noErr;