Stop using shell::GetInstance()->system_tray() in system tray items

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 6361529f8448798a6063310228fa3a620f136eb6..72c1aea15e8c635cf4e3503604e92a32507d6a76 100644
--- a/ash/system/tray/system_tray_item.h
+++ b/ash/system/tray/system_tray_item.h
@@ -17,13 +17,15 @@ class View;
 
 namespace ash {
 
+class SystemTray;

[msw, 2012/11/16 17:10:06]

nit: this forward decl should make a lot of the others unnecessary.
(many of the files touched include this file)

[bartfab (slow), 2012/11/16 17:16:01]

It does make them unnecessary in that the forward declaration happens to be
pulled in, sometimes via multiple steps of inclusion. However, as the style
guide rule is to directly include (or forward declare) all that you use, I
explicitly forward declared the class in the other headers as well.

On 2012/11/16 17:10:06, msw wrote:

[msw, 2012/11/16 17:41:35]

True, but for some straightforward cases, you can skip this. For example, not
every user of ui/gfx/rect.h needs to include point.h and size.h for those
fundamental underpinnings of Rect. That said, it's just a nit, and you're free
to ignore me :)

[stevenjb, 2012/11/16 17:41:43]

I mentioned this earlier also. Forward declarations work like #incldues. If A
includes B which includes C, A does not always need to include C (e.g. if A
derives from B derives from C, generally A only includes B). Use good judgement
here. In this case, SystemTray is part of the constructor for SystemTrayItem, so
anything that includes system_tray_item.h can safely assume that SystemTray will
remain declared; the declaration can not be removed without changing the
constructor and thus all dependent files.

[bartfab (slow), 2012/11/16 18:45:34]

Done.

+
 namespace internal {
 class TrayItemView;
 }
 
 class ASH_EXPORT SystemTrayItem {
  public:
-  SystemTrayItem();
+  explicit SystemTrayItem(SystemTray* system_tray);
   virtual ~SystemTrayItem();
 
   // Create* functions may return NULL if nothing should be displayed for the
@@ -100,7 +102,12 @@ class ASH_EXPORT SystemTrayItem {
   // the launcher is in the auto-hide state. Default is true.
   virtual bool ShouldShowLauncher() const;
 
+  // Returns the system tray that this item belongs to.
+  SystemTray* system_tray() const { return system_tray_; }
+
  private:
+  SystemTray* system_tray_;
+
   DISALLOW_COPY_AND_ASSIGN(SystemTrayItem);
 };