ash: Add a bluetooth entry in the uber tray.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 395d2bf6a3582c00dc5f3b8be6ad74899a6472a1..7ae055d1282a6f828ea126476a4e0baad2552419 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -314,6 +314,10 @@ class DummySystemTrayDelegate : public SystemTrayDelegate {
 
   virtual void RequestLockScreen() OVERRIDE {}
 
+  virtual BluetoothDeviceList GetAvailableBluetoothDevices() OVERRIDE {
+    return BluetoothDeviceList();
+  }
+
   virtual NetworkIconInfo GetMostRelevantNetworkIcon(bool large) OVERRIDE {
     return NetworkIconInfo();
   }