ash: Add a bluetooth entry in the uber tray.

ash/system/tray/system_tray.h

Index: ash/system/tray/system_tray.h
diff --git a/ash/system/tray/system_tray.h b/ash/system/tray/system_tray.h
index 526bc320a706d523e970a3c8d1d82031de648bbe..42b203b6c5ff645bbee3e6c5f43edc65eb036a7b 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -19,6 +19,7 @@ namespace ash {
 
 class AccessibilityObserver;
 class AudioObserver;
+class BluetoothObserver;
 class BrightnessObserver;
 class CapsLockObserver;
 class ClockObserver;
@@ -66,6 +67,9 @@ class ASH_EXPORT SystemTray : public views::View,
   AudioObserver* audio_observer() const {
     return audio_observer_;
   }
+  BluetoothObserver* bluetooth_observer() const {
+    return bluetooth_observer_;
+  }
   BrightnessObserver* brightness_observer() const {
     return brightness_observer_;
   }
@@ -115,6 +119,7 @@ class ASH_EXPORT SystemTray : public views::View,
   // These observers are not owned by the tray.
   AccessibilityObserver* accessibility_observer_;
   AudioObserver* audio_observer_;
+  BluetoothObserver* bluetooth_observer_;
   BrightnessObserver* brightness_observer_;
   CapsLockObserver* caps_lock_observer_;
   ClockObserver* clock_observer_;