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 f06062d9710bc0b60c591b737ea04c479dca23dd..f38318011b1f0a52d4fff77306685dfe515eab5a 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;
@@ -65,6 +66,9 @@ 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_;
   }
@@ -111,6 +115,7 @@ 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_;