Consolidate volume control code.

ash/system/tray/system_tray_item.h

Index: ash/system/tray/system_tray_item.h
diff --git a/ash/system/tray/system_tray_item.h b/ash/system/tray/system_tray_item.h
index 3c8f12f8316fcb0b3c4ae1992b96f3729cfd292a..2287979629b8413c578b71647941b8dbd7dfd195 100644
--- a/ash/system/tray/system_tray_item.h
+++ b/ash/system/tray/system_tray_item.h
@@ -67,6 +67,9 @@ class ASH_EXPORT SystemTrayItem {
   // The default implementation does nothing.
   virtual void UpdateAfterShelfAlignmentChange(ShelfAlignment alignment);
 
+  // Updates the tray view after the ash shell has been initialized.
+  virtual void UpdateAfterAshInit();

[sadrul, 2012/08/09 18:05:33]

I don't think we should have this. Or if we do have this, we should get rid of
GetInitialVisibility.

Ideally, all the things that the tray depends on, i.e. the volume-controller
etc., should be created with the tray-delegate (i.e. before the tray itself is
created), so that this problem does not show up. (perhaps create the
VolumeController etc. when the SystemTrayDelegate is created) What do you think?

[jennyz, 2012/08/13 23:26:17]

yes, I think your suggestion is reasonable. Now I move the VolumeControlDelegate
to SystemTrayDelegate, and removed UpdateAfterAshInit. Also I created a
DummyVolumeControlDelegate to be initialized by DummySystemTrayDelegate which
makes ash_unittests happy. I think we probably should do the same refactoring to
other device control delegate, such as BrightnessControlDelegate, etc. What do
you think?

+
   // Shows the detailed view for this item. If the main popup for the tray is
   // currently visible, then making this call would use the existing window to
   // display the detailed item. The detailed item will inherit the bounds of the