Move common notification layout to base class

ash/system/network/tray_sms.h

Index: ash/system/network/tray_sms.h
diff --git a/ash/system/network/tray_sms.h b/ash/system/network/tray_sms.h
index fcdd99352e4b553990fc3d2fe6d2e627f8c30762..e6861f4d5811889ffdb5d24bd9886a0a4a5ff317 100644
--- a/ash/system/network/tray_sms.h
+++ b/ash/system/network/tray_sms.h
@@ -6,13 +6,15 @@
 #define ASH_SYSTEM_NETWORK_TRAY_SMS_H
 #pragma once
 
-#include "ash/system/tray/tray_image_item.h"
+#include <string>
+
+#include "ash/system/tray/system_tray_item.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace ash {
 namespace internal {
 
-class TraySms : public TrayImageItem {
+class TraySms : public SystemTrayItem {
  public:
   TraySms();
   virtual ~TraySms();
@@ -36,6 +38,10 @@ class TraySms : public TrayImageItem {
   class SmsNotificationView;
   class SmsObserver;
 
+  // Gets the most recent message. Returns false if no messages or unable to
+  // retrieve the numebr and text from the message.
+  bool GetLatestMessage(size_t* index, std::string* number, std::string* text);
+
   // Called when sms messages have changed (by tray::SmsObserver).
   void Update(bool notify);