chrome.audio API: treat mute as system wide property

extensions/test/data/api_test/audio/input_mute_change/background.js

Index: extensions/test/data/api_test/audio/input_mute_change/background.js
diff --git a/extensions/test/data/api_test/audio/input_mute_change/background.js b/extensions/test/data/api_test/audio/input_mute_change/background.js
index 39fbc86adec937ed62f4c0d811e3693a29e7ed50..7dd7b6b05ad56fb53da7a190572143aab80f2e7a 100644
--- a/extensions/test/data/api_test/audio/input_mute_change/background.js
+++ b/extensions/test/data/api_test/audio/input_mute_change/background.js
@@ -10,6 +10,12 @@ chrome.test.runTests([
           chrome.test.assertTrue(isInput);
           chrome.test.assertTrue(isMuted);
         });
+    chrome.test.listenOnce(
+        chrome.audio.onMuteStateChanged,
+        function(evt) {
+          chrome.test.assertEq('INPUT', evt.streamType);
+          chrome.test.assertTrue(evt.value);
+        });
   }
 ]);