Bug 1530715 - P17: Move get_volume out of AudioUnitStream. r=padenot

By moving get_volume out of AudioUnitStream, we can avoid unnecessary
borrowing from the AudioUnitStream variable. This change will make the
get_volume become symmetric to the set_volume.

Differential Revision: https://phabricator.services.mozilla.com/D34050

--HG--
extra : moz-landing-system : lando

media/libcubeb/cubeb-coreaudio-rs/README_MOZILLA

@@ -3,4 +3,4 @@ git repository using the update.sh script.
 
 The cubeb-coreaudio-rs git repository is: https://github.com/ChunMinChang/cubeb-coreaudio-rs
 
-The git commit ID used was 7b054f81e09ea9f825671e731785d96decd7c488 (2019-06-21 14:40:23 -0700)
+The git commit ID used was cc7ef2614d4cfb9c03811da76902ea776b3333e2 (2019-06-21 14:40:29 -0700)

media/libcubeb/cubeb-coreaudio-rs/src/backend/mod.rs

@@ -274,6 +274,24 @@ fn set_volume(unit: AudioUnit, volume: f32) -> Result<()> {
     }
 }
 
+fn get_volume(unit: AudioUnit) -> Result<f32> {
+    assert!(!unit.is_null());
+    let mut volume: f32 = 0.0;
+    let r = audio_unit_get_parameter(
+        unit,
+        kHALOutputParam_Volume,
+        kAudioUnitScope_Global,
+        0,
+        &mut volume,
+    );
+    if r == NO_ERR {
+        Ok(volume)
+    } else {
+        cubeb_log!("AudioUnitGetParameter/kHALOutputParam_Volume rv={}", r);
+        Err(Error::error())
+    }
+}
+
 fn audiounit_make_silent(io_data: &mut AudioBuffer) {
     assert!(!io_data.mData.is_null());
     let bytes = unsafe {
@@ -3092,7 +3110,7 @@ impl<'ctx> AudioUnitStream<'ctx> {
             let vol_rv = if self.output_unit.is_null() {
                 Err(Error::error())
             } else {
-                self.get_volume()
+                get_volume(self.output_unit)
             };
 
             self.close();
@@ -4269,23 +4287,6 @@ impl<'ctx> AudioUnitStream<'ctx> {
         }
     }
 
-    fn get_volume(&self) -> Result<f32> {
-        assert!(!self.output_unit.is_null());
-        let mut volume: f32 = 0.0;
-        let r = audio_unit_get_parameter(
-            self.output_unit,
-            kHALOutputParam_Volume,
-            kAudioUnitScope_Global,
-            0,
-            &mut volume,
-        );
-        if r != NO_ERR {
-            cubeb_log!("AudioUnitGetParameter/kHALOutputParam_Volume rv={}", r);
-            return Err(Error::error());
-        }
-        Ok(volume)
-    }
-
     fn destroy(&mut self) {
         if !self.shutdown.load(Ordering::SeqCst) {
             self.stop_internal();