ash: Update the volume icon when audio is muted/unmuted.

ash/system/audio/tray_volume.cc

Index: ash/system/audio/tray_volume.cc
diff --git a/ash/system/audio/tray_volume.cc b/ash/system/audio/tray_volume.cc
index 5a8e856e27b80aab79fd18f9455043be7e847d3f..45d1d1d72f8ab5e01aaec12ac95d25af4258779e 100644
--- a/ash/system/audio/tray_volume.cc
+++ b/ash/system/audio/tray_volume.cc
@@ -115,6 +115,10 @@ class VolumeView : public views::View,
 
   void SetVolumeLevel(float percent) {
     slider_->SetValue(percent);
+    // It is possible that the volume was (un)muted, but the actual volume level
+    // did not change. In that case, setting the value of the slider won't
+    // trigger a repaint. So explicitly trigger a repaint.
+    icon_->SchedulePaint();
   }
 
  private: